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#include "types.h"
#include "bigdeal.h"
#include <memory.h>
static char rcsid[] = "$Header: /home/sater/bridge/bigdeal/RCS/mp.c,v 1.10 2000/08/16 15:06:05 sater Exp $";
/*
* Multiple precision arithmetic
* Format is 12 byte number( 96 bits), with lowest byte most significant
* (socalled bigendian format)
*/
void
mp96_zero(byte *b)
/*
* Sets b to zero
*/
{
memset(b, 0, L);
}
void
mp96_one(byte *b)
/*
* Sets b to one
*/
{
memset(b, 0, L-1);
b[L-1] = 1;
}
void
mp96_assign(byte *b, byte *b1)
/*
* Assign b1 to b
*/
{
memcpy(b, b1, L);
}
int
mp96_add(byte *b,byte *b1,byte *b2)
/*
* Computes b=b1+b2
* returns carry bit signifying overflow
*/
{
int i;
unsigned int h,carry;
carry = 0;
for (i=L-1; i>=0; i--) {
h = b1[i]+b2[i]+carry;
carry = h>=256 ? 1 : 0;
b[i] = h; /* Truncates to 8 bits automatically */
}
return carry;
}
int
mp96_sub(byte *b,byte *b1,byte *b2)
/*
* Computes b=b1-b2
* returns borrow bit signifying overflow
*/
{
int i,h;
unsigned int borrow;
borrow = 0;
for (i=L-1; i>=0; i--) {
h = b1[i]-b2[i]-borrow;
borrow = h<0 ? 1 : 0;
b[i] = h;
}
return borrow;
}
int
mp96_cmp(byte *b1, byte *b2)
/*
* Compares b1 with b2
* returns >0 when b1>b2, <0 when b1<b2, 0 when b1==b2
*/
{
int i;
int diff;
for (i=0; i<L; i++) {
diff = b1[i] - b2[i];
if (diff)
return diff;
}
return 0;
}
void
mp96_mul(byte *b,byte *b1,byte *b2)
/*
* Computes b=b1*b2
* overflow goes undetected
*/
{
int i,j;
unsigned int h,carry;
byte b1copy[L],b2copy[L],bpart[L];
/*
* Make copies of input in case one of the inputs is also output
*/
mp96_assign(b1copy, b1);
mp96_assign(b2copy, b2);
/*
* Here if an input is also output the input gets overwritten
*/
mp96_zero(b);
for (i=L-1; i>=0; i--) {
for (j=L-1; j>i; j--)
bpart[j] = 0;
carry=0;
for (j=i; j>=0; j--) {
h = b1copy[i]*b2copy[L-1+j-i]+carry;
carry = h/256;
bpart[j] = h;
}
(void) mp96_add(b,b,bpart);
}
}
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