c语言把2个8位合并为16位,汇编如何将两个8位数据合并成一个16位且为（a7b7a6b6a5b5……a0b0）?...
short foo(char a_8,char b_8) {short a_16=a_8,b_16=b_8;short a=0,b=0,result;for(short i=0,mask=1;i<8;i++){a+=(a_16&mask)<b+=(b_16&mask)<printf("%d,%d\n",a_16&mask,a_16);mask<<
short foo(char a_8,char b_8) {
short a_16=a_8,b_16=b_8;
short a=0,b=0,result;
for(short i=0,mask=1;i<8;i++){
a+=(a_16&mask)<
b+=(b_16&mask)<
printf("%d,%d\n",a_16&mask,a_16);
mask<<=1;
}
result=a<<1+b;
return result;
}
gcc
foo(char, char):
push rbp
mov rbp, rsp
mov eax, edi
mov edx, esi
mov BYTE PTR [rbp-20], al
mov eax, edx
mov BYTE PTR [rbp-24], al
movsx ax, BYTE PTR [rbp-20]
mov WORD PTR [rbp-10], ax
movsx ax, BYTE PTR [rbp-24]
mov WORD PTR [rbp-12], ax
mov WORD PTR [rbp-2], 0
mov WORD PTR [rbp-4], 0
mov WORD PTR [rbp-6], 0
mov WORD PTR [rbp-8], 1
.L3:
cmp WORD PTR [rbp-6], 7
jg .L2
movzx eax, WORD PTR [rbp-10]
and ax, WORD PTR [rbp-8]
movsx edx, ax
movsx eax, WORD PTR [rbp-6]
mov ecx, eax
sal edx, cl
mov eax, edx
mov edx, eax
movzx eax, WORD PTR [rbp-2]
add eax, edx
mov WORD PTR [rbp-2], ax
movzx eax, WORD PTR [rbp-12]
and ax, WORD PTR [rbp-8]
movsx edx, ax
movsx eax, WORD PTR [rbp-6]
mov ecx, eax
sal edx, cl
mov eax, edx
mov edx, eax
movzx eax, WORD PTR [rbp-4]
add eax, edx
mov WORD PTR [rbp-4], ax
movsx eax, WORD PTR [rbp-8]
add eax, eax
mov WORD PTR [rbp-8], ax
movzx eax, WORD PTR [rbp-6]
add eax, 1
mov WORD PTR [rbp-6], ax
jmp .L3
.L2:
movsx edx, WORD PTR [rbp-2]
movsx eax, WORD PTR [rbp-4]
add eax, 1
mov ecx, eax
sal edx, cl
mov eax, edx
mov WORD PTR [rbp-14], ax
movzx eax, WORD PTR [rbp-14]
pop rbp
ret
clang
foo(char, char): # @foo(char, char)
push rbp
mov rbp, rsp
mov al, sil
mov cl, dil
mov byte ptr [rbp - 1], cl
mov byte ptr [rbp - 2], al
movsx esi, byte ptr [rbp - 1]
mov dx, si
mov word ptr [rbp - 4], dx
movsx esi, byte ptr [rbp - 2]
mov dx, si
mov word ptr [rbp - 6], dx
mov word ptr [rbp - 8], 0
mov word ptr [rbp - 10], 0
mov word ptr [rbp - 14], 0
mov word ptr [rbp - 16], 1
.LBB0_1: # =>This Inner Loop Header: Depth=1
movsx eax, word ptr [rbp - 14]
cmp eax, 8
jge .LBB0_4
movsx eax, word ptr [rbp - 4]
movsx ecx, word ptr [rbp - 16]
and eax, ecx
movsx ecx, word ptr [rbp - 14]
shl eax, cl
movsx edx, word ptr [rbp - 8]
add edx, eax
mov si, dx
mov word ptr [rbp - 8], si
movsx eax, word ptr [rbp - 6]
movsx edx, word ptr [rbp - 16]
and eax, edx
movsx ecx, word ptr [rbp - 14]
shl eax, cl
movsx edx, word ptr [rbp - 10]
add edx, eax
mov si, dx
mov word ptr [rbp - 10], si
movsx eax, word ptr [rbp - 16]
shl eax, 1
mov si, ax
mov word ptr [rbp - 16], si
mov ax, word ptr [rbp - 14]
add ax, 1
mov word ptr [rbp - 14], ax
jmp .LBB0_1
.LBB0_4:
movsx eax, word ptr [rbp - 8]
movsx ecx, word ptr [rbp - 10]
add ecx, 1
shl eax, cl
mov dx, ax
mov word ptr [rbp - 12], dx
movsx eax, word ptr [rbp - 12]
pop rbp
ret
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