/*
 * Copyright 2021 ByteDance Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "native.h"

static const char *CS_ARRAY  = "[]{},\"[]{},\"[]{}";
static const char *CS_OBJECT = "[]{},:\"[]{}:,\"[]";

static const uint64_t ODD_MASK  = 0xaaaaaaaaaaaaaaaa;
static const uint64_t EVEN_MASK = 0x5555555555555555;

static const double P10_TAB[23] = {
    /* <= the connvertion to double is not exact when less than 1 => */     1e-000,
    1e+001, 1e+002, 1e+003, 1e+004, 1e+005, 1e+006, 1e+007, 1e+008, 1e+009, 1e+010,
    1e+011, 1e+012, 1e+013, 1e+014, 1e+015, 1e+016, 1e+017, 1e+018, 1e+019, 1e+020,
    1e+021, 1e+022 /* <= the connvertion to double is not exact when larger,  => */
};

static inline uint64_t add32(uint64_t v1, uint64_t v2, uint64_t *vo) {
    uint32_t v;
    uint32_t c = __builtin_uadd_overflow((uint32_t)v1, (uint32_t)v2, &v);

    /* set the carry */
    *vo = c;
    return v;
}

static inline uint64_t add64(uint64_t v1, uint64_t v2, uint64_t *vo) {
    uint64_t v;
    uint64_t c = __builtin_uaddll_overflow(v1, v2, &v);

    /* set the carry */
    *vo = c;
    return v;
}

static inline char isspace(char ch) {
    return ch == ' ' || ch == '\r' || ch == '\n' | ch == '\t';
}

const int MASK_USE_NUMBER = 1<<1;

static inline void vdigits(const GoString *src, long *p, JsonState *ret, uint64_t flag) {
    --*p;
    if (flag & MASK_USE_NUMBER) {
        long i = skip_number(src, p);
        if (i < 0) {
            ret->vt = i;
            return;
        }
        ret->vt = V_DOUBLE;
        ret->ep = i;
        return;
    }
    vnumber(src, p, ret);
}

static inline char advance_ns(const GoString *src, long *p) {
    size_t       vi = *p;
    size_t       nb = src->len;
    const char * sp = src->buf;

    /* it's likely to run into non-spaces within a few
     * characters, so test up to 4 characters manually */
    if (vi < nb && !isspace(sp[vi])) goto nospace; else vi++;
    if (vi < nb && !isspace(sp[vi])) goto nospace; else vi++;
    if (vi < nb && !isspace(sp[vi])) goto nospace; else vi++;
    if (vi < nb && !isspace(sp[vi])) goto nospace; else vi++;

    /* check EOF */
    if (vi >= nb) {
        *p = vi;
        return 0;
    }

    /* too many spaces, use SIMD to search for characters */
    if ((vi = lspace(sp, nb, vi)) >= nb) {
        return 0;
    }

nospace:
    *p = vi + 1;
    return src->buf[vi];
}

static inline int64_t advance_dword(const GoString *src, long *p, long dec, int64_t ret, uint32_t val) {
    if (*p > src->len + dec - 4) {
        *p = src->len;
        return -ERR_EOF;
    } else if (*(uint32_t *)(src->buf + *p - dec) == val) {
        *p += 4 - dec;
        return ret;
    } else {
        *p -= dec;
        for (int i = 0; src->buf[*p] == (val & 0xff); i++, ++*p) { val >>= 8; }
        return -ERR_INVAL;
    }
}

static inline ssize_t advance_string(const GoString *src, long p, int64_t *ep) {
    char     ch;
    uint64_t es;
    uint64_t fe;
    uint64_t os;
    uint64_t m0;
    uint64_t m1;
    uint64_t cr = 0;

    /* prevent out-of-bounds accessing */
    if (unlikely(src->len == p)) {
        return -ERR_EOF;
    }

    /* buffer pointers */
    size_t       nb = src->len;
    const char * sp = src->buf;
    const char * ss = src->buf;

#define ep_init()   *ep = -1;
#define ep_setc()   ep_setx(sp - ss - 1)
#define ep_setx(x)  if (*ep == -1) { *ep = (x); }

    /* seek to `p` */
    nb -= p;
    sp += p;
    ep_init()

#if USE_AVX2
    /* initialize vectors */
    __m256i v0;
    __m256i v1;
    __m256i q0;
    __m256i q1;
    __m256i x0;
    __m256i x1;
    __m256i cq = _mm256_set1_epi8('"');
    __m256i cx = _mm256_set1_epi8('\\');

    /* partial masks */
    uint32_t s0;
    uint32_t s1;
    uint32_t t0;
    uint32_t t1;
#else
    /* initialize vectors */
    __m128i v0;
    __m128i v1;
    __m128i v2;
    __m128i v3;
    __m128i q0;
    __m128i q1;
    __m128i q2;
    __m128i q3;
    __m128i x0;
    __m128i x1;
    __m128i x2;
    __m128i x3;
    __m128i cq = _mm_set1_epi8('"');
    __m128i cx = _mm_set1_epi8('\\');

    /* partial masks */
    uint32_t s0;
    uint32_t s1;
    uint32_t s2;
    uint32_t s3;
    uint32_t t0;
    uint32_t t1;
    uint32_t t2;
    uint32_t t3;
#endif

#define m0_mask(add)                \
    m1 &= ~cr;                      \
    fe  = (m1 << 1) | cr;           \
    os  = (m1 & ~fe) & ODD_MASK;    \
    es  = add(os, m1, &cr) << 1;    \
    m0 &= ~(fe & (es ^ EVEN_MASK));

    /* 64-byte SIMD loop */
    while (likely(nb >= 64)) {
#if USE_AVX2
        v0 = _mm256_loadu_si256   ((const void *)(sp +  0));
        v1 = _mm256_loadu_si256   ((const void *)(sp + 32));
        q0 = _mm256_cmpeq_epi8    (v0, cq);
        q1 = _mm256_cmpeq_epi8    (v1, cq);
        x0 = _mm256_cmpeq_epi8    (v0, cx);
        x1 = _mm256_cmpeq_epi8    (v1, cx);
        s0 = _mm256_movemask_epi8 (q0);
        s1 = _mm256_movemask_epi8 (q1);
        t0 = _mm256_movemask_epi8 (x0);
        t1 = _mm256_movemask_epi8 (x1);
        m0 = ((uint64_t)s1 << 32) | (uint64_t)s0;
        m1 = ((uint64_t)t1 << 32) | (uint64_t)t0;
#else
        v0 = _mm_loadu_si128   ((const void *)(sp +  0));
        v1 = _mm_loadu_si128   ((const void *)(sp + 16));
        v2 = _mm_loadu_si128   ((const void *)(sp + 32));
        v3 = _mm_loadu_si128   ((const void *)(sp + 48));
        q0 = _mm_cmpeq_epi8    (v0, cq);
        q1 = _mm_cmpeq_epi8    (v1, cq);
        q2 = _mm_cmpeq_epi8    (v2, cq);
        q3 = _mm_cmpeq_epi8    (v3, cq);
        x0 = _mm_cmpeq_epi8    (v0, cx);
        x1 = _mm_cmpeq_epi8    (v1, cx);
        x2 = _mm_cmpeq_epi8    (v2, cx);
        x3 = _mm_cmpeq_epi8    (v3, cx);
        s0 = _mm_movemask_epi8 (q0);
        s1 = _mm_movemask_epi8 (q1);
        s2 = _mm_movemask_epi8 (q2);
        s3 = _mm_movemask_epi8 (q3);
        t0 = _mm_movemask_epi8 (x0);
        t1 = _mm_movemask_epi8 (x1);
        t2 = _mm_movemask_epi8 (x2);
        t3 = _mm_movemask_epi8 (x3);
        m0 = ((uint64_t)s3 << 48) | ((uint64_t)s2 << 32) | ((uint64_t)s1 << 16) | (uint64_t)s0;
        m1 = ((uint64_t)t3 << 48) | ((uint64_t)t2 << 32) | ((uint64_t)t1 << 16) | (uint64_t)t0;
#endif

        /** update first quote position */
        if (unlikely(m1 != 0)) {
            ep_setx(sp - ss + __builtin_ctzll(m1))
        }

        /** mask all the escaped quotes */
        if (unlikely(m1 != 0 || cr != 0)) {
            m0_mask(add64)
        }

        /* check for end quote */
        if (m0 != 0) {
            return sp - ss + __builtin_ctzll(m0) + 1;
        }

        /* move to the next block */
        sp += 64;
        nb -= 64;
    }

    /* 32-byte SIMD round */
    if (likely(nb >= 32)) {
#if USE_AVX2
        v0 = _mm256_loadu_si256   ((const void *)sp);
        q0 = _mm256_cmpeq_epi8    (v0, cq);
        x0 = _mm256_cmpeq_epi8    (v0, cx);
        s0 = _mm256_movemask_epi8 (q0);
        t0 = _mm256_movemask_epi8 (x0);
        m0 = (uint64_t)s0;
        m1 = (uint64_t)t0;
#else
        v0 = _mm_loadu_si128   ((const void *)(sp +  0));
        v1 = _mm_loadu_si128   ((const void *)(sp + 16));
        q0 = _mm_cmpeq_epi8    (v0, cq);
        q1 = _mm_cmpeq_epi8    (v1, cq);
        x0 = _mm_cmpeq_epi8    (v0, cx);
        x1 = _mm_cmpeq_epi8    (v1, cx);
        s0 = _mm_movemask_epi8 (q0);
        s1 = _mm_movemask_epi8 (q1);
        t0 = _mm_movemask_epi8 (x0);
        t1 = _mm_movemask_epi8 (x1);
        m0 = ((uint64_t)s1 << 16) | (uint64_t)s0;
        m1 = ((uint64_t)t1 << 16) | (uint64_t)t0;
#endif

        /** update first quote position */
        if (unlikely(m1 != 0)) {
            ep_setx(sp - ss + __builtin_ctzll(m1))
        }

        /** mask all the escaped quotes */
        if (unlikely(m1 != 0 || cr != 0)) {
            m0_mask(add32)
        }

        /* check for end quote */
        if (m0 != 0) {
            return sp - ss + __builtin_ctzll(m0) + 1;
        }

        /* move to the next block */
        sp += 32;
        nb -= 32;
    }

    /* check for carry */
    if (unlikely(cr != 0)) {
        if (nb == 0) {
            return -ERR_EOF;
        } else {
            ep_setc()
            sp++, nb--;
        }
    }

    /* handle the remaining bytes with scalar code */
    while (nb-- > 0 && (ch = *sp++) != '"') {
        if (unlikely(ch == '\\')) {
            if (nb == 0) {
                return -ERR_EOF;
            } else {
                ep_setc()
                sp++, nb--;
            }
        }
    }

#undef ep_init
#undef ep_setc
#undef ep_setx
#undef m0_mask

    /* check for quotes */
    if (ch == '"') {
        return sp - ss;
    } else {
        return -ERR_EOF;
    }
}

static inline int _mm_get_mask(__m128i v, __m128i t) {
    return _mm_movemask_epi8(_mm_cmpeq_epi8(v, t));
}

// contrl char: 0x00 ~ 0x1F
static inline int _mm_cchars_mask(__m128i v) {
    __m128i e1 = _mm_cmpgt_epi8 (v, _mm_set1_epi8(-1));
    __m128i e2 = _mm_cmpgt_epi8 (v, _mm_set1_epi8(31));
    return    _mm_movemask_epi8 (_mm_andnot_si128 (e2, e1));
}

#if USE_AVX2

static inline int _mm256_get_mask(__m256i v, __m256i t) {
    return _mm256_movemask_epi8(_mm256_cmpeq_epi8(v, t));
}

// contrl char: 0x00 ~ 0x1F
static inline int _mm256_cchars_mask(__m256i v) {
    __m256i e1 = _mm256_cmpgt_epi8 (v, _mm256_set1_epi8(-1));
    __m256i e2 = _mm256_cmpgt_epi8 (v, _mm256_set1_epi8(31));
    return    _mm256_movemask_epi8 (_mm256_andnot_si256 (e2, e1));
}

#endif

static inline ssize_t advance_validate_string(const GoString *src, long p, int64_t *ep) {
    char     ch;
    uint64_t es;
    uint64_t fe;
    uint64_t os;
    uint64_t m0;
    uint64_t m1;
    uint64_t m2;
    uint64_t cr = 0;
    long     qp = 0;
    long     np = 0;

    /* prevent out-of-bounds accessing */
    if (unlikely(src->len == p)) {
        return -ERR_EOF;
    }

    /* buffer pointers */
    size_t       nb = src->len;
    const char * sp = src->buf;
    const char * ss = src->buf;

#define ep_init()   *ep = -1;
#define ep_setc()   ep_setx(sp - ss - 1)
#define ep_setx(x)  if (*ep == -1) { *ep = (x); }

    /* seek to `p` */
    nb -= p;
    sp += p;
    ep_init()

#if USE_AVX2
    /* initialize vectors */
    __m256i v0;
    __m256i v1;
    __m256i cq = _mm256_set1_epi8('"');
    __m256i cx = _mm256_set1_epi8('\\');

    /* partial masks */
    uint32_t s0, s1;
    uint32_t t0, t1;
    uint32_t c0, c1;
#else
    /* initialize vectors */
    __m128i v0;
    __m128i v1;
    __m128i v2;
    __m128i v3;
    __m128i cq = _mm_set1_epi8('"');
    __m128i cx = _mm_set1_epi8('\\');

    /* partial masks */
    uint32_t s0, s1, s2, s3;
    uint32_t t0, t1, t2, t3;
    uint32_t c0, c1, c2, c3;
#endif

#define m0_mask(add)                \
    m1 &= ~cr;                      \
    fe  = (m1 << 1) | cr;           \
    os  = (m1 & ~fe) & ODD_MASK;    \
    es  = add(os, m1, &cr) << 1;    \
    m0 &= ~(fe & (es ^ EVEN_MASK));

    /* 64-byte SIMD loop */
    while (likely(nb >= 64)) {
#if USE_AVX2
        v0 = _mm256_loadu_si256   ((const void *)(sp +  0));
        v1 = _mm256_loadu_si256   ((const void *)(sp + 32));
        s0 = _mm256_get_mask(v0, cq);
        s1 = _mm256_get_mask(v1, cq);
        t0 = _mm256_get_mask(v0, cx);
        t1 = _mm256_get_mask(v1, cx);
        c0 = _mm256_cchars_mask(v0);
        c1 = _mm256_cchars_mask(v1);
        m0 = ((uint64_t)s1 << 32) | (uint64_t)s0;
        m1 = ((uint64_t)t1 << 32) | (uint64_t)t0;
        m2 = ((uint64_t)c1 << 32) | (uint64_t)c0;
#else
        v0 = _mm_loadu_si128   ((const void *)(sp +  0));
        v1 = _mm_loadu_si128   ((const void *)(sp + 16));
        v2 = _mm_loadu_si128   ((const void *)(sp + 32));
        v3 = _mm_loadu_si128   ((const void *)(sp + 48));
        s0 = _mm_get_mask(v0, cq);
        s1 = _mm_get_mask(v1, cq);
        s2 = _mm_get_mask(v2, cq);
        s3 = _mm_get_mask(v3, cq);
        t0 = _mm_get_mask(v0, cx);
        t1 = _mm_get_mask(v1, cx);
        t2 = _mm_get_mask(v2, cx);
        t3 = _mm_get_mask(v3, cx);
        c0 = _mm_cchars_mask(v0);
        c1 = _mm_cchars_mask(v1);
        c2 = _mm_cchars_mask(v2);
        c3 = _mm_cchars_mask(v3);
        m0 = ((uint64_t)s3 << 48) | ((uint64_t)s2 << 32) | ((uint64_t)s1 << 16) | (uint64_t)s0;
        m1 = ((uint64_t)t3 << 48) | ((uint64_t)t2 << 32) | ((uint64_t)t1 << 16) | (uint64_t)t0;
        m2 = ((uint64_t)c3 << 48) | ((uint64_t)c2 << 32) | ((uint64_t)c1 << 16) | (uint64_t)c0;

#endif

        /** update first quote position */
        if (unlikely(m1 != 0)) {
            ep_setx(sp - ss + __builtin_ctzll(m1))
        }

        /** mask all the escaped quotes */
        if (unlikely(m1 != 0 || cr != 0)) {
            m0_mask(add64)
        }

        /* get the position of end quote */
        if (m0 != 0) {
            qp = sp - ss + __builtin_ctzll(m0) + 1;
            /* check control chars in JSON string */
            if (unlikely(m2 !=0 && (np = sp - ss + __builtin_ctzll(m2)) < qp)) {
                ep_setx(np) // set error position
                return -ERR_INVAL;
            }
            return qp;
        }

        /* check control chars in JSON string */
        if (unlikely(m2 != 0)) {
            ep_setx(sp - ss + __builtin_ctzll(m2))
            return -ERR_INVAL;
        }

        /* move to the next block */
        sp += 64;
        nb -= 64;
    }

    /* 32-byte SIMD round */
    if (likely(nb >= 32)) {
#if USE_AVX2
        v0 = _mm256_loadu_si256   ((const void *)sp);
        s0 = _mm256_get_mask (v0, cq);
        t0 = _mm256_get_mask (v0, cx);
        c0 = _mm256_cchars_mask(v0);
        m0 = (uint64_t)s0;
        m1 = (uint64_t)t0;
        m2 = (uint64_t)c0;
#else
        v0 = _mm_loadu_si128   ((const void *)(sp +  0));
        v1 = _mm_loadu_si128   ((const void *)(sp + 16));
        s0 = _mm_get_mask(v0, cq);
        s1 = _mm_get_mask(v1, cq);
        t0 = _mm_get_mask(v0, cx);
        t1 = _mm_get_mask(v1, cx);
        c0 = _mm_cchars_mask(v0);
        c1 = _mm_cchars_mask(v1);
        m0 = ((uint64_t)s1 << 16) | (uint64_t)s0;
        m1 = ((uint64_t)t1 << 16) | (uint64_t)t0;
        m2 = ((uint64_t)c1 << 16) | (uint64_t)c0;
#endif

        /** update first quote position */
        if (unlikely(m1 != 0)) {
            ep_setx(sp - ss + __builtin_ctzll(m1))
        }

        /** mask all the escaped quotes */
        if (unlikely(m1 != 0 || cr != 0)) {
            m0_mask(add32)
        }

        /* get the position of end quote */
        if (m0 != 0) {
            qp = sp - ss + __builtin_ctzll(m0) + 1;
            /* check control chars in JSON string */
            if (unlikely(m2 !=0 && (np = sp - ss + __builtin_ctzll(m2)) < qp)) {
                ep_setx(np) // set error position
                return -ERR_INVAL;
            }
            return qp;
        }

        /* check control chars in JSON string */
        if (unlikely(m2 != 0)) {
            ep_setx(sp - ss + __builtin_ctzll(m2))
            return -ERR_INVAL;
        }

        /* move to the next block */
        sp += 32;
        nb -= 32;
    }

    /* check for carry */
    if (unlikely(cr != 0)) {
        if (nb == 0) {
            return -ERR_EOF;
        } else {
            ep_setc()
            sp++, nb--;
        }
    }

    /* handle the remaining bytes with scalar code */
    while (nb-- > 0 && (ch = *sp++) != '"') {
        if (unlikely(ch == '\\')) {
            if (nb == 0) {
                return -ERR_EOF;
            } else {
                ep_setc()
                sp++, nb--;
            }
        } else if (unlikely( ch >= 0 && ch <= 0x1f)) { // control chars
            ep_setc()
            return -ERR_INVAL;
        }
    }

#undef ep_init
#undef ep_setc
#undef ep_setx
#undef m0_mask

    /* check for quotes */
    if (ch == '"') {
        return sp - ss;
    } else {
        return -ERR_EOF;
    }
}

/** Value Scanning Routines **/

const uint64_t MASK_ALLOW_CONTROL = 1ul<<31;

long value(const char *s, size_t n, long p, JsonState *ret, uint64_t flags) {
    long     q = p;
    GoString m = {.buf = s, .len = n};
    bool allow_control = (flags&MASK_ALLOW_CONTROL) != 0;

    /* parse the next identifier, q is UNSAFE, may cause out-of-bounds accessing */
    switch (advance_ns(&m, &q)) {
        case '-' : /* fallthrough */
        case '0' : /* fallthrough */
        case '1' : /* fallthrough */
        case '2' : /* fallthrough */
        case '3' : /* fallthrough */
        case '4' : /* fallthrough */
        case '5' : /* fallthrough */
        case '6' : /* fallthrough */
        case '7' : /* fallthrough */
        case '8' : /* fallthrough */
        case '9' : vdigits(&m, &q, ret, flags)                          ; return q;
        case '"' : vstring(&m, &q, ret)                                 ; return q;
        case 'n' : ret->vt = advance_dword(&m, &q, 1, V_NULL, VS_NULL)  ; return q;
        case 't' : ret->vt = advance_dword(&m, &q, 1, V_TRUE, VS_TRUE)  ; return q;
        case 'f' : ret->vt = advance_dword(&m, &q, 0, V_FALSE, VS_ALSE) ; return q;
        case '[' : ret->vt = V_ARRAY                                    ; return q;
        case '{' : ret->vt = V_OBJECT                                   ; return q;
        case ':' : ret->vt = allow_control ? V_KEY_SEP : -ERR_INVAL     ; return allow_control ? q : q - 1;
        case ',' : ret->vt = allow_control ? V_ELEM_SEP : -ERR_INVAL    ; return allow_control ? q : q - 1;
        case ']' : ret->vt = allow_control ? V_ARRAY_END : -ERR_INVAL   ; return allow_control ? q : q - 1;
        case '}' : ret->vt = allow_control ? V_OBJECT_END : -ERR_INVAL  ; return allow_control ? q : q - 1;
        case  0  : ret->vt = V_EOF                                      ; return q;
        default  : ret->vt = -ERR_INVAL                                 ; return q - 1;
    }
}

void vstring(const GoString *src, long *p, JsonState *ret) {
    int64_t v = -1;
    int64_t i = *p;
    ssize_t e = advance_string(src, i, &v);

    /* check for errors */
    if (e < 0) {
        *p = src->len;
        ret->vt = e;
        return;
    }

    /* update the result, and fix the escape position (escaping past the end of string) */
    *p = e;
    ret->iv = i;
    ret->vt = V_STRING;
    ret->ep = v >= e ? -1 : v;
}

#define set_vt(t)   \
    ret->vt = t;

#define init_ret(t) \
    ret->vt = t;    \
    ret->dv = 0.0;  \
    ret->iv = 0;    \
    ret->ep = *p;

#define check_eof()         \
    if (i >= n) {           \
        *p = n;             \
        ret->vt = -ERR_EOF; \
        return;             \
    }

#define check_sign(on_neg)  \
    if (s[i] == '-') {      \
        i++;                \
        on_neg;             \
        check_eof()         \
    }

#define check_digit()               \
    if (s[i] < '0' || s[i] > '9') { \
        *p = i;                     \
        ret->vt = -ERR_INVAL;       \
        return;                     \
    }

#define check_leading_zero()                                                                    \
    if (s[i] == '0' && (i >= n || (s[i + 1] != '.' && s[i + 1] != 'e' && s[i + 1] != 'E'))) {   \
        *p = ++i;                                                                               \
        return;                                                                                 \
    }

#define parse_sign(sgn)                 \
    if (s[i] == '+' || s[i] == '-') {   \
        sgn = s[i++] == '+' ? 1 : -1;   \
        check_eof()                     \
    }

#define is_digit(val) \
    '0' <= val && val <= '9'

#define add_integer_to_mantissa(man, man_nd, exp10, dig) \
    if (man_nd < 19) {                                   \
        man = man * 10 + dig;                            \
        man_nd++;                                        \
    } else {                                             \
        exp10++;                                         \
    }

#define add_float_to_mantissa(man, man_nd, exp10, dig) \
    man = man * 10 + dig;                              \
    man_nd++;                                          \
    exp10--;

#define parse_float_digits(val, sgn, ...)                       \
    while (i < n && s[i] >= '0' && s[i] <= '9' __VA_ARGS__) {   \
        val *= 10;                                              \
        val += sgn * (s[i++] - '0');                            \
    }

#define parse_integer_digits(val, sgn, ovf)                     \
    while (i < n && s[i] >= '0' && s[i] <= '9') {               \
        if (add_digit_overflow(val, sgn * (s[i++] - '0'))) {    \
            ovf = 1;                                            \
            break;                                              \
        }                                                       \
    }

#define add_digit_overflow(val, chr) (          \
    __builtin_mul_overflow(val, 10, &val) ||    \
    __builtin_add_overflow(val, chr, &val)      \
)

#define vinteger(type, sgn, on_neg)                     \
    int  ovf = 0;                                       \
    type val = 0;                                       \
                                                        \
    /* initial buffer pointers */                       \
    long         i = *p;                                \
    size_t       n = src->len;                          \
    const char * s = src->buf;                          \
                                                        \
    /* initialize the result, and check for '-' */      \
    init_ret(V_INTEGER)                                 \
    check_eof()                                         \
    check_sign(on_neg)                                  \
                                                        \
    /* check for leading zero or any digits */          \
    check_digit()                                       \
    check_leading_zero()                                \
    parse_integer_digits(val, sgn, ovf)                 \
                                                        \
    /* check for overflow */                            \
    if (ovf) {                                          \
        *p = i - 1;                                     \
        ret->vt = -ERR_OVERFLOW;                        \
        return;                                         \
    }                                                   \
                                                        \
    /* check for the decimal part */                    \
    if (i < n && s[i] == '.') {                         \
        *p = i;                                         \
        ret->vt = -ERR_NUMBER_FMT;                      \
        return;                                         \
    }                                                   \
                                                        \
    /* check for the exponent part */                   \
    if (i < n && (s[i] == 'e' || s[i] == 'E')) {        \
        *p = i;                                         \
        ret->vt = -ERR_NUMBER_FMT;                      \
        return;                                         \
    }                                                   \
                                                        \
    /* update the result */                             \
    *p = i;                                             \
    ret->iv = val;

/** check whether float can represent the val exactly **/
static inline bool is_atof_exact(uint64_t man, int exp, int sgn, double *val) {
    *val = (double)man;

    if (man >> 52 != 0) {
        return false;
    }

    /* equal to if (sgn == -1) { *val *= -1; } */
    *(uint64_t *)val |= ((uint64_t)(sgn) >> 63 << 63);

    if (exp == 0 || man == 0) {
        return true;
    } else if (exp > 0 && exp <= 15+22) {
        /* uint64 integers: accurate range <= 10^15          *
         * Powers of 10: accurate range <= 10^22, as P10_TAB *
         * Example: man 1, exp 36, is ok                     */
        if (exp > 22) {
            *val *= P10_TAB[exp-22];
            exp = 22;
        }

        /* f is not accurate when too larger */
        if (*val > 1e15 || *val < -1e15) {
            return false;
        }

        *val *= P10_TAB[exp];
        return true;
    } else if (exp < 0 && exp >= -22) {
        *val /=  P10_TAB[-exp];
        return true;
    }

    return false;
}

static inline double atof_fast(uint64_t man, int exp, int sgn, int trunc, double *val) {
    double val_up = 0.0;

    /* look-up for fast atof if the conversion can be exactly */
    if (is_atof_exact(man, exp, sgn, val)) {
        return true;
    }

    /* A fast atof algorithm for high percison */
    if (atof_eisel_lemire64(man, exp, sgn, val)) {
        if (!trunc || (atof_eisel_lemire64(man+1, exp, sgn, &val_up) && val_up == *val)) {
            return true;
        }
    }

    return false;
}

static bool inline is_overflow(uint64_t man, int sgn, int exp10) {
    /* the former exp10 != 0 means man has overflowed
     * the later euqals to man*sgn < INT64_MIN or > INT64_MAX */
    return exp10 != 0 ||
        ((man >> 63) == 1 && ((uint64_t)sgn & man) != (1ull << 63));
}

void vnumber(const GoString *src, long *p, JsonState *ret) {
    int      sgn = 1;
    uint64_t man = 0; // mantissa for double (float64)
    int   man_nd = 0; // # digits of mantissa, 10 ^ 19 fits uint64_t
    int    exp10 = 0; // val = sgn * man * 10 ^ exp10
    int    trunc = 0;
    double   val = 0;

    /* initial buffer pointers */
    long         i = *p;
    size_t       n = src->len;
    const char * s = src->buf;
    char     *dbuf = ret->dbuf;
    ssize_t   dcap = ret->dcap;

    /* initialize the result, and check for EOF */
    init_ret(V_INTEGER)
    check_eof()
    check_sign(sgn = -1)

    /* check for leading zero */
    check_digit()
    check_leading_zero()

    /* parse the integer part */
    while (i < n && is_digit(s[i])) {
        add_integer_to_mantissa(man, man_nd, exp10, (s[i] - '0'))
        i++;
    }

    if (exp10 > 0) {
        trunc = 1;
    }

    /* check for decimal points */
    if (i < n && s[i] == '.') {
        i++;
        set_vt(V_DOUBLE)
        check_eof()
        check_digit()
    }

    /* skip the leading zeros of 0.000xxxx */
    if (man == 0 && exp10 == 0) {
        while (i < n && s[i] == '0') {
            i++;
            exp10--;
        }
        man = 0;
        man_nd = 0;
    }

    /* the fractional part (uint64_t mantissa can represent at most 19 digits) */
    while (i < n && man_nd < 19 && is_digit(s[i])) {
        add_float_to_mantissa(man, man_nd, exp10, (s[i] - '0'))
        i++;
    }

     /* skip the remaining digits */
    while (i < n && is_digit(s[i])) {
        trunc = 1;
        i++;
    }

    /* check for exponent */
    if (i < n && (s[i] == 'e' || s[i] == 'E')) {
        int esm = 1;
        int exp = 0;

        /* check for the '+' or '-' sign, and parse the power */
        i++;
        set_vt(V_DOUBLE)
        check_eof()
        parse_sign(esm)
        check_digit()
        while (i < n && is_digit(s[i])) {
            if (exp < 10000) {
                exp = exp * 10 + (s[i] - '0');
            }
            i++;
        }
        exp10 += exp * esm;
        goto parse_float;
    }

    if (ret->vt == V_INTEGER) {
        if (!is_overflow(man, sgn, exp10)) {
            ret->iv = (int64_t)man * sgn;

            /* following lines equal to ret->dv = (double)(man) * sgn */
            ret->dv = (double)(man);
            *(uint64_t *)&ret->dv |= ((uint64_t)(sgn) >> 63 << 63);

            *p = i;
            return;
        }
        set_vt(V_DOUBLE)
    }

parse_float:
    /* when fast algorithms failed, use slow fallback.*/
    if(!atof_fast(man, exp10, sgn, trunc, &val)) {
        val = atof_native(s + *p, i - *p, dbuf, dcap);
    }

    /* check parsed double val */
    if (is_infinity(val)) {
        ret->vt = -ERR_FLOAT_INF;
    }

    /* update the result */
    ret->dv = val;
    *p = i;
}

void vsigned(const GoString *src, long *p, JsonState *ret) {
    int64_t sgn = 1;
    vinteger(int64_t, sgn, sgn = -1)
}

void vunsigned(const GoString *src, long *p, JsonState *ret) {
    vinteger(uint64_t, 1, {
        *p = i - 1;
        ret->vt = -ERR_NUMBER_FMT;
        return;
    })
}

#undef init_ret
#undef check_eof
#undef check_digit
#undef check_leading_zero
#undef parse_sign
#undef is_digit
#undef add_integer_to_mantissa
#undef add_float_to_mantissa
#undef parse_float_digits
#undef parse_integer_digits
#undef add_digit_overflow
#undef vinteger

/** Value Skipping FSM **/

#define FSM_VAL         0
#define FSM_ARR         1
#define FSM_OBJ         2
#define FSM_KEY         3
#define FSM_ELEM        4
#define FSM_ARR_0       5
#define FSM_OBJ_0       6

#define FSM_DROP(v)     (v)->sp--
#define FSM_REPL(v, t)  (v)->vt[(v)->sp - 1] = (t)

#define FSM_CHAR(c)     do { if (ch != (c)) return -ERR_INVAL; } while (0)
#define FSM_XERR(v)     do { long r = (v); if (r < 0) return r; } while (0)

static inline void fsm_init(StateMachine *self, int vt) {
    self->sp = 1;
    self->vt[0] = vt;
}

static inline long fsm_push(StateMachine *self, int vt) {
    if (self->sp >= MAX_RECURSE) {
        return -ERR_RECURSE_MAX;
    } else {
        self->vt[self->sp++] = vt;
        return 0;
    }
}

#define VALID_DEFAULT 0 // basic validate, except JSON string.
#define VALID_FULL    1 // also validate JSON string, including control chars or invalid UTF-8.

static inline long fsm_exec(StateMachine *self, const GoString *src, long *p, int validate_flag) {
    int  vt;
    char ch;
    long vi = -1;

    /* run until no more nested values */
    while (self->sp) {
        ch = advance_ns(src, p);
        vt = self->vt[self->sp - 1];

        /* set the start address if any */
        if (vi == -1) {
            vi = *p - 1;
        }

        /* check for special types */
        switch (vt) {
            default: {
                FSM_DROP(self);
                break;
            }

            /* arrays */
            case FSM_ARR: {
                switch (ch) {
                    case ']' : FSM_DROP(self);                    continue;
                    case ',' : FSM_XERR(fsm_push(self, FSM_VAL)); continue;
                    default  : return -ERR_INVAL;
                }
            }

            /* objects */
            case FSM_OBJ: {
                switch (ch) {
                    case '}' : FSM_DROP(self);                    continue;
                    case ',' : FSM_XERR(fsm_push(self, FSM_KEY)); continue;
                    default  : return -ERR_INVAL;
                }
            }

            /* object keys */
            case FSM_KEY: {
                FSM_CHAR('"');
                FSM_REPL(self, FSM_ELEM);
                FSM_XERR(skip_string(src, p));
                continue;
            }

            /* object element */
            case FSM_ELEM: {
                FSM_CHAR(':');
                FSM_REPL(self, FSM_VAL);
                continue;
            }

            /* arrays, first element */
            case FSM_ARR_0: {
                if (ch == ']') {
                    FSM_DROP(self);
                    continue;
                } else {
                    FSM_REPL(self, FSM_ARR);
                    break;
                }
            }

            /* objects, first pair */
            case FSM_OBJ_0: {
                switch (ch) {
                    default: {
                        return -ERR_INVAL;
                    }

                    /* empty object */
                    case '}': {
                        FSM_DROP(self);
                        continue;
                    }

                    /* the quote of the first key */
                    case '"': {
                        FSM_REPL(self, FSM_OBJ);
                        if (validate_flag == VALID_DEFAULT) {
                            FSM_XERR(skip_string(src, p));
                        } else if (validate_flag == VALID_FULL) {
                            FSM_XERR(validate_string(src, p));
                        }
                        FSM_XERR(fsm_push(self, FSM_ELEM));
                        continue;
                    }
                }
            }
        }

        /* simple values */
        switch (ch) {
            case '0' : /* fallthrough */
            case '1' : /* fallthrough */
            case '2' : /* fallthrough */
            case '3' : /* fallthrough */
            case '4' : /* fallthrough */
            case '5' : /* fallthrough */
            case '6' : /* fallthrough */
            case '7' : /* fallthrough */
            case '8' : /* fallthrough */
            case '9' : FSM_XERR(skip_positive(src, p));                     break;
            case '-' : FSM_XERR(skip_negative(src, p));                     break;
            case 'n' : FSM_XERR(advance_dword(src, p, 1, *p - 1, VS_NULL)); break;
            case 't' : FSM_XERR(advance_dword(src, p, 1, *p - 1, VS_TRUE)); break;
            case 'f' : FSM_XERR(advance_dword(src, p, 0, *p - 1, VS_ALSE)); break;
            case '[' : FSM_XERR(fsm_push(self, FSM_ARR_0));                 break;
            case '{' : FSM_XERR(fsm_push(self, FSM_OBJ_0));                 break;
            case '"' : {
                if (validate_flag == VALID_DEFAULT) {
                    FSM_XERR(skip_string(src, p));
                } else if (validate_flag == VALID_FULL) {
                    FSM_XERR(validate_string(src, p));
                }
                break;
            }
            case  0  : return -ERR_EOF;
            default  : return -ERR_INVAL;
        }
    }

    /* all done */
    return vi;
}

#undef FSM_DROP
#undef FSM_REPL
#undef FSM_CHAR
#undef FSM_XERR

#define check_bits(mv)                              \
    if (unlikely((v = mv & (mv - 1)) != 0)) {       \
        return -(sp - ss + __builtin_ctz(v) + 1);   \
    }

#define check_sidx(iv)          \
    if (likely(iv == -1)) {     \
        iv = sp - ss - 1;       \
    } else {                    \
        return -(sp - ss);      \
    }

#define check_vidx(iv, mv)                              \
    if (mv != 0) {                                      \
        if (likely(iv == -1)) {                         \
            iv = sp - ss + __builtin_ctz(mv);           \
        } else {                                        \
            return -(sp - ss + __builtin_ctz(mv) + 1);  \
        }                                               \
    }

static inline long do_skip_number(const char *sp, size_t nb) {
    long         di = -1;
    long         ei = -1;
    long         si = -1;
    const char * ss = sp;

    /* check for EOF */
    if (nb == 0) {
        return -1;
    }

    /* special case of '0' */
    if (*sp == '0' && (nb == 1 || (sp[1] != '.' && sp[1] != 'e' && sp[1] != 'E'))) {
        return 1;
    }

#if USE_AVX2
    /* can do with AVX-2 */
    if (likely(nb >= 32)) {
        __m256i d9 = _mm256_set1_epi8('9');
        __m256i ds = _mm256_set1_epi8('/');
        __m256i dp = _mm256_set1_epi8('.');
        __m256i el = _mm256_set1_epi8('e');
        __m256i eu = _mm256_set1_epi8('E');
        __m256i xp = _mm256_set1_epi8('+');
        __m256i xm = _mm256_set1_epi8('-');

        /* 32-byte loop */
        do {
            __m256i sb = _mm256_loadu_si256  ((const void *)sp);
            __m256i i0 = _mm256_cmpgt_epi8   (sb, ds);
            __m256i i9 = _mm256_cmpgt_epi8   (sb, d9);
            __m256i id = _mm256_cmpeq_epi8   (sb, dp);
            __m256i il = _mm256_cmpeq_epi8   (sb, el);
            __m256i iu = _mm256_cmpeq_epi8   (sb, eu);
            __m256i ip = _mm256_cmpeq_epi8   (sb, xp);
            __m256i im = _mm256_cmpeq_epi8   (sb, xm);
            __m256i iv = _mm256_andnot_si256 (i9, i0);
            __m256i ie = _mm256_or_si256     (il, iu);
            __m256i is = _mm256_or_si256     (ip, im);
            __m256i rt = _mm256_or_si256     (iv, id);
            __m256i ru = _mm256_or_si256     (ie, is);
            __m256i rv = _mm256_or_si256     (rt, ru);

            /* exponent and sign position */
            uint32_t md = _mm256_movemask_epi8(id);
            uint32_t me = _mm256_movemask_epi8(ie);
            uint32_t ms = _mm256_movemask_epi8(is);
            uint32_t mr = _mm256_movemask_epi8(rv);

            /* mismatch position */
            uint32_t v;
            uint32_t i = __builtin_ctzll(~(uint64_t)mr | 0x0100000000);

            /* mask out excess characters */
            if (i != 32) {
                md &= (1 << i) - 1;
                me &= (1 << i) - 1;
                ms &= (1 << i) - 1;
            }

            /* check & update decimal point, exponent and sign index */
            check_bits(md)
            check_bits(me)
            check_bits(ms)
            check_vidx(di, md)
            check_vidx(ei, me)
            check_vidx(si, ms)

            /* check for valid number */
            if (i != 32) {
                sp += i;
                _mm256_zeroupper();
                goto check_index;
            }

            /* move to next block */
            sp += 32;
            nb -= 32;
        } while (nb >= 32);

        /* clear the upper half to prevent AVX-SSE transition penalty */
        _mm256_zeroupper();
    }
#endif

    /* can do with SSE */
    if (likely(nb >= 16)) {
        __m128i dc = _mm_set1_epi8(':');
        __m128i ds = _mm_set1_epi8('/');
        __m128i dp = _mm_set1_epi8('.');
        __m128i el = _mm_set1_epi8('e');
        __m128i eu = _mm_set1_epi8('E');
        __m128i xp = _mm_set1_epi8('+');
        __m128i xm = _mm_set1_epi8('-');

        /* 16-byte loop */
        do {
            __m128i sb = _mm_loadu_si128 ((const void *)sp);
            __m128i i0 = _mm_cmpgt_epi8  (sb, ds);
            __m128i i9 = _mm_cmplt_epi8  (sb, dc);
            __m128i id = _mm_cmpeq_epi8  (sb, dp);
            __m128i il = _mm_cmpeq_epi8  (sb, el);
            __m128i iu = _mm_cmpeq_epi8  (sb, eu);
            __m128i ip = _mm_cmpeq_epi8  (sb, xp);
            __m128i im = _mm_cmpeq_epi8  (sb, xm);
            __m128i iv = _mm_and_si128   (i9, i0);
            __m128i ie = _mm_or_si128    (il, iu);
            __m128i is = _mm_or_si128    (ip, im);
            __m128i rt = _mm_or_si128    (iv, id);
            __m128i ru = _mm_or_si128    (ie, is);
            __m128i rv = _mm_or_si128    (rt, ru);

            /* exponent and sign position */
            uint32_t md = _mm_movemask_epi8(id);
            uint32_t me = _mm_movemask_epi8(ie);
            uint32_t ms = _mm_movemask_epi8(is);
            uint32_t mr = _mm_movemask_epi8(rv);

            /* mismatch position */
            uint32_t v;
            uint32_t i = __builtin_ctzll(~mr | 0x00010000);

            /* mask out excess characters */
            if (i != 16) {
                md &= (1 << i) - 1;
                me &= (1 << i) - 1;
                ms &= (1 << i) - 1;
            }

            /* check & update exponent and sign index */
            check_bits(md)
            check_bits(me)
            check_bits(ms)
            check_vidx(di, md)
            check_vidx(ei, me)
            check_vidx(si, ms)

            /* check for valid number */
            if (i != 16) {
                sp += i;
                goto check_index;
            }

            /* move to next block */
            sp += 16;
            nb -= 16;
        } while (nb >= 16);
    }

    /* remaining bytes, do with scalar code */
    while (likely(nb-- > 0)) {
        switch (*sp++) {
            case '0' : /* fallthrough */
            case '1' : /* fallthrough */
            case '2' : /* fallthrough */
            case '3' : /* fallthrough */
            case '4' : /* fallthrough */
            case '5' : /* fallthrough */
            case '6' : /* fallthrough */
            case '7' : /* fallthrough */
            case '8' : /* fallthrough */
            case '9' : break;
            case '.' : check_sidx(di); break;
            case 'e' : /* fallthrough */
            case 'E' : check_sidx(ei); break;
            case '+' : /* fallthrough */
            case '-' : check_sidx(si); break;
            default  : sp--; goto check_index;
        }
    }
check_index:
    if (di == 0 || si == 0 || ei == 0) {
        return -1;
    } else if (di == sp - ss - 1|| si == sp - ss - 1 || ei == sp - ss - 1) {
        return -(sp - ss);
    } else if (si > 0 && ei != si - 1) {
        return -si - 1;
    } else if (di >= 0 && ei >= 0 && di > ei - 1) {
        return -di - 1;
    } else if (di >= 0 && ei >= 0 && di == ei - 1) {
        return -ei - 1;
    } else {
        return sp - ss;
    }
}

#undef check_bits
#undef check_sidx
#undef check_vidx

long skip_one(const GoString *src, long *p, StateMachine *m) {
    fsm_init(m, FSM_VAL);
    return fsm_exec(m, src, p, VALID_DEFAULT);
}

long skip_array(const GoString *src, long *p, StateMachine *m) {
    fsm_init(m, FSM_ARR_0);
    return fsm_exec(m, src, p, VALID_DEFAULT);
}

long skip_object(const GoString *src, long *p, StateMachine *m) {
    fsm_init(m, FSM_OBJ_0);
    return fsm_exec(m, src, p, VALID_DEFAULT);
}

long skip_string(const GoString *src, long *p) {
    int64_t v;
    ssize_t q = *p - 1;
    ssize_t e = advance_string(src, *p, &v);

    /* check for errors, and update the position */
    if (e >= 0) {
        *p = e;
        return q;
    } else {
        *p = src->len;
        return e;
    }
}

long validate_string(const GoString *src, long *p) {
    int64_t v;
    ssize_t q = *p - 1;
    ssize_t e = advance_validate_string(src, *p, &v);

    /* check for errors in string advance */
    if (e < 0) {
        *p = e == -ERR_EOF ? src->len : v;
        return e;
    }

    /* check for errors in UTF-8 validate */
    ssize_t nb = e - *p - 1;
    ssize_t r = utf8_validate(src->buf + *p, nb);
    if (r >= 0) {
        *p += r;
        return -ERR_INVAL;
    }
    *p = e;
    return q;
}

long skip_negative(const GoString *src, long *p) {
    long i = *p;
    long r = do_skip_number(src->buf + i, src->len - i);

    /* check for errors */
    if (r < 0) {
        *p -= r + 1;
        return -ERR_INVAL;
    }

    /* update value pointer */
    *p += r;
    return i - 1;
}

long skip_positive(const GoString *src, long *p) {
    long i = *p - 1;
    long r = do_skip_number(src->buf + i, src->len - i);

    /* check for errors */
    if (r < 0) {
        *p -= r + 2;
        return -ERR_INVAL;
    }

    /* update value pointer */
    *p += r - 1;
    return i;
}

long skip_number(const GoString *src, long *p) {
    const char* ss = src->buf;
    const char* sp = src->buf + *p;
    size_t nb = src->len;
    long i = *p;
    long r;
    bool neg = *sp == '-';

    sp += neg;
    nb -= neg;
    if (unlikely(nb <= 0)) {
        *p = sp - ss;
        return -ERR_EOF;
    }

    if (unlikely(i < nb && (*sp > '9' || *sp < '0'))) {
        *p = sp - ss;
        return -ERR_INVAL;
    }

    r = do_skip_number(sp, nb);
    if (unlikely(r < 0)) {
        *p = sp - (r + 1) - ss;
        return -ERR_INVAL;
    }
    *p = sp + r - ss;
    return i;
}

long validate_one(const GoString *src, long *p, StateMachine *m) {
    fsm_init(m, FSM_VAL);
    return fsm_exec(m, src, p, VALID_FULL);
}