idigitaddsubmult.c

Arithmetic for integers of almost unlimited size for C and C++. Developed and copyrighted by Ra

/* idigitaddsubmult.c - inline assembler code for MSVC++6.0 on Intel586 */
/* TPf, Sep 1999 */

#include <iint.h>
#include <idigit.h>

#if !defined(USE_C_DIGITADD)
DigitType 
DigitAdd(sum, a, b, carry)
    DigitType *sum, a, b, carry;
 /*
    *sum=LOW-DIGIT(a+b+carry); return HIGH-DIGIT(a+b+carry);
 */
{
__asm
    {
/*	.text
	.align 4
	.globl USCORE(DigitAdd)
USCORE(DigitAdd):	*/
	mov ebx, sum		; &sum -> ebx
	mov ecx, a		; a -> ecx
	mov edx, b		; b -> edx
	mov eax, carry		; carry -> eax
	shr eax,1		; carry -> carry-bit
	adc ecx,edx		; a + b + carry-bit -> ecx (former a)
	rcl eax,1		; high order bit -> carry	
	mov DWORD PTR [ebx], ecx	; a + b + carry-bit -> *sum
    }
}
#endif

#if !defined(USE_C_DIGITSUB)
DigitType 
DigitSub(diff, a, b, carry)
    DigitType *diff, a, b, carry;
 /*
    *diff=RESULT; return CARRY; where RESULT, CARRY are defined by:
    2^BitsPerDigit > CARRY*2^BitsPerDigit + a - b - carry == RESULT >= 0
 */
{
__asm
    {
/* 	.align 4
	.globl USCORE(DigitSub)
USCORE(DigitSub): */
	mov ebx, diff
	mov edx, a
	mov ecx, b
	mov eax, carry
	shr eax,1
	sbb edx,ecx
	rcl eax,1
	mov DWORD PTR [ebx], edx
    }
}
#endif

#if !defined(USE_C_DIGITMULT)
DigitType 
DigitMult(prod, a, b)
    DigitType *prod, a, b;
 /*
    *prod=LOW-DIGIT(a*b); return HIGH-DIGIT(a*b);
 */
{
__asm
    {	    
/*	.align 4
	.globl USCORE(DigitMult)
USCORE(DigitMult): */
	mov ebx, prod
	mov eax, a
	mov ecx, b
	mul ecx
        mov DWORD PTR [ebx], eax
	mov eax,edx
    }
}
#endif

#if !defined(USE_C_DIGITMULTADD)
DigitType 
DigitMultAdd(prod, a, b, carry)
    DigitType *prod, a, b, carry;
 /*
    *prod=LOW-DIGIT(a*b+carry); return HIGH-DIGIT(a*b+carry);
 */
{
__asm
    {
/*	.align 4
	.globl USCORE(DigitMultAdd)
USCORE(DigitMultAdd): */
	mov ebx, prod
	mov eax, a
	mov edx, b
	mul edx
	mov ecx, carry
	add eax,ecx
	adc edx,0
        mov eax, [ebx]
	mov eax,edx
    }
}
#endif