我想要一个包含4个字节地址和4个字节数据的寄存器。为此，我考虑过将其构建为结构数组（包含地址和数据作为成员）或矩阵中。这里是一个示例代码，用于测试我想要实现的目标：
#include <stdio.h>
#include <stdint.h>
void reg_init();
#define REG_SIZE 1
typedef struct Reg{
uint8_t addr[4];
uint8_t data[4];
} reg;
static reg reg_struct[REG_SIZE];
static uint8_t reg_matrix[REG_SIZE][8];
int main()
{
int index=-1;
reg_init();
for(int i=0; i<REG_SIZE; i++)
{
uint8_t addr_to_check[4]={0x12,0x34,0x56,0x78};
// FOR STRUCT
for(int j=0; j<4; j++)
{
if(addr_to_check[j]!=reg_struct[i].addr[j]) break;
if(j==3) index = i;
}
//FOR MATRIX
for(int j=0; j<4; j++)
{
if(addr_to_check[j]!=reg_matrix[i][j]) break;
if(j==3) index = i;
}
}
if (index<0) printf("Address not found\n");
else printf("Address at index: %i",index);
return 0;
}
void reg_init()
{
// Register init for testing
reg_struct[0].addr[0] = 0x12;
reg_struct[0].addr[1] = 0x34;
reg_struct[0].addr[2] = 0x56;
reg_struct[0].addr[3] = 0x78;
reg_struct[0].data[0] = 0x01;
reg_struct[0].data[1] = 0x02;
reg_struct[0].data[2] = 0x03;
reg_struct[0].data[3] = 0x04;
reg_matrix[0][0] = 0x12;
reg_matrix[0][1] = 0x34;
reg_matrix[0][2] = 0x56;
reg_matrix[0][3] = 0x78;
reg_matrix[0][4] = 0x01;
reg_matrix[0][5] = 0x02;
reg_matrix[0][6] = 0x03;
reg_matrix[0][7] = 0x04;
}
该示例仅显示了一个单位大小的寄存器，但是大小会大得多（最多8个字节）。总的来说，我对性能方面的优化很感兴趣。使用一个或另一个真的很在乎，还是编译器会构建相同的机器代码？
答案 0 :(得分：1)
下面是使用Visual Studio 2019创建的上述代码的汇编。
查看记录行号; Line 50和; Line 51，看起来编译器已经为矩阵和结构创建了相同的汇编代码。
; Listing generated by Microsoft (R) Optimizing Compiler Version 19.20.27508.1
TITLE D:\main.c
.686P
.XMM
include listing.inc
.model flat
INCLUDELIB LIBCMT
INCLUDELIB OLDNAMES
PUBLIC ___local_stdio_printf_options
PUBLIC __vfprintf_l
PUBLIC _printf
PUBLIC _reg_init
PUBLIC _main
EXTRN ___acrt_iob_func:PROC
EXTRN ___stdio_common_vfprintf:PROC
_DATA SEGMENT
COMM ?_OptionsStorage@?1??__local_stdio_printf_options@@9@9:QWORD ; `__local_stdio_printf_options'::`2'::_OptionsStorage
_DATA ENDS
_BSS SEGMENT
_reg_struct DQ 01H DUP (?)
_reg_matrix DB 08H DUP (?)
_BSS ENDS
_DATA SEGMENT
$SG8132 DB 'Address not found', 0aH, 00H
ORG $+1
$SG8133 DB 'Address at index: %i', 00H
_DATA ENDS
; Function compile flags: /Odtp
_TEXT SEGMENT
_index$ = -20 ; size = 4
_addr_to_check$1 = -16 ; size = 4
_j$2 = -12 ; size = 4
_j$3 = -8 ; size = 4
_i$4 = -4 ; size = 4
_main PROC
; File D:\main.c
; Line 16
push ebp
mov ebp, esp
sub esp, 20 ; 00000014H
; Line 17
mov DWORD PTR _index$[ebp], -1
; Line 18
call _reg_init
; Line 19
mov DWORD PTR _i$4[ebp], 0
jmp SHORT $LN4@main
$LN2@main:
mov eax, DWORD PTR _i$4[ebp]
add eax, 1
mov DWORD PTR _i$4[ebp], eax
$LN4@main:
cmp DWORD PTR _i$4[ebp], 1
jge $LN3@main
; Line 21
mov BYTE PTR _addr_to_check$1[ebp], 18 ; 00000012H
mov BYTE PTR _addr_to_check$1[ebp+1], 52 ; 00000034H
mov BYTE PTR _addr_to_check$1[ebp+2], 86 ; 00000056H
mov BYTE PTR _addr_to_check$1[ebp+3], 120 ; 00000078H
; Line 23
mov DWORD PTR _j$3[ebp], 0
jmp SHORT $LN7@main
$LN5@main:
mov ecx, DWORD PTR _j$3[ebp]
add ecx, 1
mov DWORD PTR _j$3[ebp], ecx
$LN7@main:
cmp DWORD PTR _j$3[ebp], 4
jge SHORT $LN6@main
; Line 25
mov edx, DWORD PTR _j$3[ebp]
movzx eax, BYTE PTR _addr_to_check$1[ebp+edx]
mov ecx, DWORD PTR _j$3[ebp]
mov edx, DWORD PTR _i$4[ebp]
movzx ecx, BYTE PTR _reg_struct[ecx+edx*8]
cmp eax, ecx
je SHORT $LN11@main
jmp SHORT $LN6@main
$LN11@main:
; Line 26
cmp DWORD PTR _j$3[ebp], 3
jne SHORT $LN12@main
mov edx, DWORD PTR _i$4[ebp]
mov DWORD PTR _index$[ebp], edx
$LN12@main:
; Line 27
jmp SHORT $LN5@main
$LN6@main:
; Line 30
mov DWORD PTR _j$2[ebp], 0
jmp SHORT $LN10@main
$LN8@main:
mov eax, DWORD PTR _j$2[ebp]
add eax, 1
mov DWORD PTR _j$2[ebp], eax
$LN10@main:
cmp DWORD PTR _j$2[ebp], 4
jge SHORT $LN9@main
; Line 32
mov ecx, DWORD PTR _j$2[ebp]
movzx edx, BYTE PTR _addr_to_check$1[ebp+ecx]
mov eax, DWORD PTR _j$2[ebp]
mov ecx, DWORD PTR _i$4[ebp]
movzx eax, BYTE PTR _reg_matrix[eax+ecx*8]
cmp edx, eax
je SHORT $LN13@main
jmp SHORT $LN9@main
$LN13@main:
; Line 33
cmp DWORD PTR _j$2[ebp], 3
jne SHORT $LN14@main
mov ecx, DWORD PTR _i$4[ebp]
mov DWORD PTR _index$[ebp], ecx
$LN14@main:
; Line 34
jmp SHORT $LN8@main
$LN9@main:
; Line 35
jmp $LN2@main
$LN3@main:
; Line 36
cmp DWORD PTR _index$[ebp], 0
jge SHORT $LN15@main
push OFFSET $SG8132
call _printf
add esp, 4
jmp SHORT $LN16@main
$LN15@main:
; Line 37
mov edx, DWORD PTR _index$[ebp]
push edx
push OFFSET $SG8133
call _printf
add esp, 8
$LN16@main:
; Line 38
xor eax, eax
; Line 39
mov esp, ebp
pop ebp
ret 0
_main ENDP
_TEXT ENDS
; Function compile flags: /Odtp
_TEXT SEGMENT
_reg_init PROC
; File D:\main.c
; Line 41
push ebp
mov ebp, esp
; Line 43
mov eax, 8
imul ecx, eax, 0
mov edx, 1
imul eax, edx, 0
mov BYTE PTR _reg_struct[ecx+eax], 18 ; 00000012H
; Line 44
mov ecx, 8
imul edx, ecx, 0
mov eax, 1
shl eax, 0
mov BYTE PTR _reg_struct[edx+eax], 52 ; 00000034H
; Line 45
mov ecx, 8
imul edx, ecx, 0
mov eax, 1
shl eax, 1
mov BYTE PTR _reg_struct[edx+eax], 86 ; 00000056H
; Line 46
mov ecx, 8
imul edx, ecx, 0
mov eax, 1
imul ecx, eax, 3
mov BYTE PTR _reg_struct[edx+ecx], 120 ; 00000078H
; Line 47
mov edx, 8
imul eax, edx, 0
mov ecx, 1
imul edx, ecx, 0
mov BYTE PTR _reg_struct[eax+edx+4], 1
; Line 48
mov eax, 8
imul ecx, eax, 0
mov edx, 1
shl edx, 0
mov BYTE PTR _reg_struct[ecx+edx+4], 2
; Line 49
mov eax, 8
imul ecx, eax, 0
mov edx, 1
shl edx, 1
mov BYTE PTR _reg_struct[ecx+edx+4], 3
; Line 50
mov eax, 8
imul ecx, eax, 0
mov edx, 1
imul eax, edx, 3
mov BYTE PTR _reg_struct[ecx+eax+4], 4
; Line 51
mov ecx, 8
imul edx, ecx, 0
mov eax, 1
imul ecx, eax, 0
mov BYTE PTR _reg_matrix[edx+ecx], 18 ; 00000012H
; Line 52
mov edx, 8
imul eax, edx, 0
mov ecx, 1
shl ecx, 0
mov BYTE PTR _reg_matrix[eax+ecx], 52 ; 00000034H
; Line 53
mov edx, 8
imul eax, edx, 0
mov ecx, 1
shl ecx, 1
mov BYTE PTR _reg_matrix[eax+ecx], 86 ; 00000056H
; Line 54
mov edx, 8
imul eax, edx, 0
mov ecx, 1
imul edx, ecx, 3
mov BYTE PTR _reg_matrix[eax+edx], 120 ; 00000078H
; Line 55
mov eax, 8
imul ecx, eax, 0
mov edx, 1
shl edx, 2
mov BYTE PTR _reg_matrix[ecx+edx], 1
; Line 56
mov eax, 8
imul ecx, eax, 0
mov edx, 1
imul eax, edx, 5
mov BYTE PTR _reg_matrix[ecx+eax], 2
; Line 57
mov ecx, 8
imul edx, ecx, 0
mov eax, 1
imul ecx, eax, 6
mov BYTE PTR _reg_matrix[edx+ecx], 3
; Line 58
mov edx, 8
imul eax, edx, 0
mov ecx, 1
imul edx, ecx, 7
mov BYTE PTR _reg_matrix[eax+edx], 4
; Line 59
pop ebp
ret 0
_reg_init ENDP
_TEXT ENDS
; Function compile flags: /Odtp
; COMDAT _printf
_TEXT SEGMENT
__Result$ = -8 ; size = 4
__ArgList$ = -4 ; size = 4
__Format$ = 8 ; size = 4
_printf PROC ; COMDAT
; File C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\ucrt\stdio.h
; Line 954
push ebp
mov ebp, esp
sub esp, 8
; Line 957
lea eax, DWORD PTR __Format$[ebp+4]
mov DWORD PTR __ArgList$[ebp], eax
; Line 958
mov ecx, DWORD PTR __ArgList$[ebp]
push ecx
push 0
mov edx, DWORD PTR __Format$[ebp]
push edx
push 1
call ___acrt_iob_func
add esp, 4
push eax
call __vfprintf_l
add esp, 16 ; 00000010H
mov DWORD PTR __Result$[ebp], eax
; Line 959
mov DWORD PTR __ArgList$[ebp], 0
; Line 960
mov eax, DWORD PTR __Result$[ebp]
; Line 961
mov esp, ebp
pop ebp
ret 0
_printf ENDP
_TEXT ENDS
; Function compile flags: /Odtp
; COMDAT __vfprintf_l
_TEXT SEGMENT
__Stream$ = 8 ; size = 4
__Format$ = 12 ; size = 4
__Locale$ = 16 ; size = 4
__ArgList$ = 20 ; size = 4
__vfprintf_l PROC ; COMDAT
; File C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\ucrt\stdio.h
; Line 642
push ebp
mov ebp, esp
; Line 643
mov eax, DWORD PTR __ArgList$[ebp]
push eax
mov ecx, DWORD PTR __Locale$[ebp]
push ecx
mov edx, DWORD PTR __Format$[ebp]
push edx
mov eax, DWORD PTR __Stream$[ebp]
push eax
call ___local_stdio_printf_options
mov ecx, DWORD PTR [eax+4]
push ecx
mov edx, DWORD PTR [eax]
push edx
call ___stdio_common_vfprintf
add esp, 24 ; 00000018H
; Line 644
pop ebp
ret 0
__vfprintf_l ENDP
_TEXT ENDS
; Function compile flags: /Odtp
; COMDAT ___local_stdio_printf_options
_TEXT SEGMENT
___local_stdio_printf_options PROC ; COMDAT
; File C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\ucrt\corecrt_stdio_config.h
; Line 86
push ebp
mov ebp, esp
; Line 88
mov eax, OFFSET ?_OptionsStorage@?1??__local_stdio_printf_options@@9@9 ; `__local_stdio_printf_options'::`2'::_OptionsStorage
; Line 89
pop ebp
ret 0
___local_stdio_printf_options ENDP
_TEXT ENDS
END