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HexString to Long

This function (cdecl calling convention) will convert a hex string into a long value.

Submitted By: NickDMax

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Rating:

Views: 447

Language: Assembly

Last Modified: March 29, 2009

Instructions: This is a C style function so you must pass the parameters on the stack. Push the pointer onto the stack before you call. *** added error checking will now only read 8 chars and will stop on invalid chars.

Snippet

; EXAMPLE C program:
;
; #include <stdio.h>
; #define DEBUG_TESTCASE(testCase, var) var = hex2num( testCase); \
; printf("Test: \"%15s\" = 0x%08X = %u\n",testCase, var, var);
;
;extern long hex2num(const char *);
;
; int main() {
; unsigned long a;
; DEBUG_TESTCASE("1234ABCD", a);
; DEBUG_TESTCASE("5678efab", a);
; DEBUG_TESTCASE("FfFfFfFf", a);
; DEBUG_TESTCASE("3.141593", a);
; DEBUG_TESTCASE("12345678ABCD", a);
; DEBUG_TESTCASE("JAVABABE", a);
; DEBUG_TESTCASE("CafeBabe", a);
; DEBUG_TESTCASE("0000123@", a);
; DEBUG_TESTCASE("0000123^", a);
; DEBUG_TESTCASE("10000000", a);
; DEBUG_TESTCASE( "10000", a);
; DEBUG_TESTCASE( "100", a);
; DEBUG_TESTCASE( "1", a);
; DEBUG_TESTCASE("a0000000", a);
; DEBUG_TESTCASE( "A0000", a);
; DEBUG_TESTCASE( "F00", a);
; DEBUG_TESTCASE( "f", a);
; DEBUG_TESTCASE("100\x01", a);
; return 0;
; }
.386p
PUBLIC _hex2num
MODEL flat, C
_TEXT segment dword public use32 'CODE'
_hex2num proc near ; extern "C" long hex2num(const char *ptr)
push ebp
mov ebp, esp ; set base pointer to stack pointer
push ebx
mov edx, dword ptr [ebp+8] ; place the pointer into edx
xor ebx, ebx ; zero ebx
xor ecx, ecx ; zero our return value
and eax, 0FFh ; mask eax to just al.
beginWhile: ; while (*ptr !=0)
cmp byte ptr [edx], 0 ; test to see if *ptr == 0
je short endWhile ; if so, jump over loop.
cmp ebx, 08h ; a long is only 8 bytes long
je short endWhile ; if we have read 8 chars end.
mov al, [edx] ; load a byte form the string
sub al, 30h ; al = al - '0' -- subtract 48
cmp al, 09h ; if (al <= 9) jmp doCalc
jbe doCalc
cmp al, 11h ; Check chars between '0' and 'A'
jb endWhile
sub al, 07h ; al = al - ('A' - '0') + 10 (sub al, 11h, add al, 0xA)
cmp al, 0Fh ; if (al <= 15) jmp doCalc
jbe doCalc
cmp al, 2Ah ; Check chars betweeen 'A' and 'a'
jb endWhile
sub al, 20h ; al = al - ('a' - 'A')
cmp al, 0Fh ; if (al > 15) then we have an illegal char
ja endWhile ; so we exit the proc as is.
doCalc:
add ecx, ecx ; ecx = 2 ecx
lea ecx, [8*ecx] ; ebx = 8 * ecx = 16 * original_ecx neat eh! no need for mult
add ecx, eax ; ecx += al
inc edx ; inc ptr
inc ebx ; inc count
jmp short beginWhile
endWhile:
mov eax, ecx ; return the value
pop ebx
pop ebp
ret
_hex2num endp
_TEXT ends
END

Copy & Paste

; EXAMPLE C program:
;
; #include <stdio.h>
; #define DEBUG_TESTCASE(testCase, var) var = hex2num( testCase); \
;    printf("Test: \"%15s\" = 0x%08X = %u\n",testCase, var, var);
; 
;extern long hex2num(const char *); 
;
; int main() {
;      unsigned long a;
;     DEBUG_TESTCASE("1234ABCD", a);
;     DEBUG_TESTCASE("5678efab", a);
;     DEBUG_TESTCASE("FfFfFfFf", a);
;     DEBUG_TESTCASE("3.141593", a);
;     DEBUG_TESTCASE("12345678ABCD", a);
;     DEBUG_TESTCASE("JAVABABE", a);
;     DEBUG_TESTCASE("CafeBabe", a);
;     DEBUG_TESTCASE("0000123@", a);
;     DEBUG_TESTCASE("0000123^", a);
;     DEBUG_TESTCASE("10000000", a);
;     DEBUG_TESTCASE(   "10000", a);
;     DEBUG_TESTCASE(     "100", a);
;     DEBUG_TESTCASE(       "1", a);
;     DEBUG_TESTCASE("a0000000", a);
;     DEBUG_TESTCASE(   "A0000", a);
;     DEBUG_TESTCASE(     "F00", a);
;     DEBUG_TESTCASE(       "f", a);
;     DEBUG_TESTCASE("100\x01", a);
;     return 0;
; }

.386p
PUBLIC _hex2num

MODEL flat, C
_TEXT    segment dword public use32 'CODE'

_hex2num proc near                     ; extern "C" long hex2num(const char *ptr)
    push ebp                            
    mov ebp, esp                       ; set base pointer to stack pointer
    push ebx
        mov edx, dword ptr [ebp+8]     ; place the pointer into edx
        xor ebx, ebx                   ; zero ebx
        xor ecx, ecx                   ; zero our return value
        and eax, 0FFh                  ; mask eax to just al.
beginWhile:                            ; while (*ptr !=0) 
        cmp byte ptr [edx], 0          ; test to see if *ptr == 0
        je short endWhile              ; if so, jump over loop.
        cmp ebx, 08h                   ; a long is only 8 bytes long
        je short endWhile              ; if we have read 8 chars end.
        mov al, [edx]                  ; load a byte form the string
        sub al, 30h                    ; al = al - '0' -- subtract 48

cmp al, 09h                    ; if (al <= 9) jmp doCalc
        jbe doCalc
        cmp al, 11h                    ; Check chars between '0' and 'A'
        jb endWhile
        
        sub al, 07h                    ; al = al - ('A' - '0') + 10 (sub al, 11h, add al, 0xA)
        cmp al, 0Fh                    ; if (al <= 15) jmp doCalc
        jbe doCalc
        cmp al, 2Ah                    ; Check chars betweeen 'A' and 'a'
        jb endWhile
        
        sub al, 20h                    ; al = al - ('a' - 'A')
        
        cmp al, 0Fh                    ; if (al > 15) then we have an illegal char
        ja endWhile                    ;   so we exit the proc as is.
        
doCalc:        
        add ecx, ecx                   ; ecx = 2 ecx
        lea ecx, [8*ecx]               ; ebx = 8 * ecx = 16 * original_ecx neat eh! no need for mult
        add ecx, eax                   ; ecx += al
        inc edx                        ; inc ptr
        inc ebx                        ; inc count
        jmp short beginWhile
endWhile:
        mov eax, ecx                   ; return the value
    pop ebx
    pop ebp
    ret
_hex2num endp

_TEXT    ends

END