CHAPTER 42. STRING TO NUMBER CONVERSION (ATOI()) CHAPTER 42. STRING TO NUMBER CONVERSION (ATOI())
printf ("%d\n", my_atoi ("-a1234567890")); // error
};
42.2.1 Optimizing GCC 4.9.1 x64
Listing 42.6: Optimizing GCC 4.9.1 x64.LC0:
.string "Error! Unexpected char: '%c'\n"
my_atoi:
sub rsp, 8
movsx edx, BYTE PTR [rdi]
; check for minus sign
cmp dl, 45 ; '-'
je .L22
xor esi, esi
test dl, dl
je .L20
.L10:
; ESI=0 here if there was no minus sign and 1 if it was
lea eax, [rdx-48]
; any character other than digit will result unsigned number greater than 9 after subtraction
; so if it is not digit, jump to L4, where error will be reported:
cmp al, 9
ja .L4
xor eax, eax
jmp .L6
.L7:
lea ecx, [rdx-48]
cmp cl, 9
ja .L4
.L6:
lea eax, [rax+rax4]
add rdi, 1
lea eax, [rdx-48+rax2]
movsx edx, BYTE PTR [rdi]
test dl, dl
jne .L7
; if there was no minus sign, skip NEG instruction
; if it was, execute it.
test esi, esi
je .L18
neg eax
.L18:
add rsp, 8
ret
.L22:
movsx edx, BYTE PTR [rdi+1]
lea rax, [rdi+1]
test dl, dl
je .L20
mov rdi, rax
mov esi, 1
jmp .L10
.L20:
xor eax, eax
jmp .L18
.L4:
; report error. character is in EDX
mov edi, 1
mov esi, OFFSET FLAT:.LC0 ; "Error! Unexpected char: '%c'\n"
xor eax, eax
call __printf_chk
xor edi, edi
call exit