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thank you Marc G.

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Perry Kivolowitz 2022-12-26 13:25:00 -06:00
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section_1/regs/ldr.md
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@ -187,25 +187,25 @@ Here is a hand translation of the above `C` code for function `Sum()`:
.global Sum // 1 .global Sum // 1
.text // 2 .text // 2
.align 4 // 3 .align 4 // 3
// 4
// x0 is the pointer to data // 5 // x0 is the pointer to data // 5
// x1 is the length and is reused as `end` // 6 // x1 is the length and is reused as `end` // 6
// x2 is the sum // 7 // x2 is the sum // 7
// x3 is the current dereferenced value // 8 // x3 is the current dereferenced value // 8
// 9
Sum: // 10 Sum: // 10
mov x2, xzr // 11 mov x2, xzr // 11
add x1, x0, x1, lsl 3 // 12 add x1, x0, x1, lsl 3 // 12
b 2f // 13 b 2f // 13
// 14
1: ldr x3, [x0], 8 // 15 1: ldr x3, [x0], 8 // 15
add x2, x2, x3 // 16 add x2, x2, x3 // 16
2: cmp x0, x1 // 17 2: cmp x0, x1 // 17
blt 1b // 18 blt 1b // 18
// 19
mov x0, x2 // 20 mov x0, x2 // 20
ret // 21 ret // 21
// 22
.end // 23 .end // 23
``` ```
@ -372,22 +372,22 @@ Here is a more elaborate case study. Given this:
```c ```c
#include <stdio.h> /* 1 */ #include <stdio.h> /* 1 */
/* 2 */
struct Person /* 3 */ struct Person /* 3 */
{ /* 4 */ { /* 4 */
char * fname; /* 5 */ char * fname; /* 5 */
char * lname; /* 6 */ char * lname; /* 6 */
int age; /* 7 */ int age; /* 7 */
}; /* 8 */ }; /* 8 */
/* 9 */
extern int rand(); /* 10 */ extern int rand(); /* 10 */
extern struct Person * FindOldestPerson(struct Person *, int); /* 11 */ extern struct Person * FindOldestPerson(struct Person *, int); /* 11 */
/* 12 */
struct Person * OriginalFindOldestPerson(struct Person * people, int length) /* 13 */ struct Person * OriginalFindOldestPerson(struct Person * people, int length) /* 13 */
{ /* 14 */ { /* 14 */
int oldest_age = 0; /* 15 */ int oldest_age = 0; /* 15 */
struct Person * oldest_ptr = NULL; /* 16 */ struct Person * oldest_ptr = NULL; /* 16 */
/* 17 */
if (people) /* 18 */ if (people) /* 18 */
{ /* 19 */ { /* 19 */
struct Person * end_ptr = people + length; /* 20 */ struct Person * end_ptr = people + length; /* 20 */
@ -403,9 +403,9 @@ struct Person * OriginalFindOldestPerson(struct Person * people, int length) /*
} /* 30 */ } /* 30 */
return oldest_ptr; /* 31 */ return oldest_ptr; /* 31 */
} /* 32 */ } /* 32 */
/* 33 */
#define LENGTH 20 /* 34 */ #define LENGTH 20 /* 34 */
/* 35 */
int main() /* 36 */ int main() /* 36 */
{ /* 37 */ { /* 37 */
struct Person array[LENGTH]; /* 38 */ struct Person array[LENGTH]; /* 38 */
@ -440,9 +440,9 @@ serve only to move the location of the `age` member away from offset 0.
same name so that the linker can reconcile the reference to same name so that the linker can reconcile the reference to
`FindOldestPerson`. `FindOldestPerson`.
`OriginalFindOldestPerson` takes a pointer to an instance of `struct Person`. Being a pointer, `OriginalFindOldestPerson` takes a pointer to an instance of `struct
this can be used as a way of finding just one instance or, as in our case, an array of these Person`. Being a pointer, this can be used as a way of finding just one
`structs`. instance or, as in our case, an array of these `structs`.
The function finds the largest value in the `age` member using the The function finds the largest value in the `age` member using the
expected algorithm. It initializes an `oldest_age` found so far with 0 expected algorithm. It initializes an `oldest_age` found so far with 0