src/libbiguint/bu_subc.c


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

/* ISC license. */

/* OpenBSD needs that for EOVERFLOW. wtfbsdseriously */
#define _BSD_SOURCE

#include <errno.h>
#include <skalibs/uint32.h>
#include <skalibs/biguint.h>

int bu_subc (uint32 *c, unsigned int cn, uint32 const *a, unsigned int an, uint32 const *b, unsigned int bn, register int carry)
{
  register unsigned int i = 0 ;
  for (; i < cn ; i++)
  {
    register uint32 ai = (i < an) ? a[i] : 0 ;
    register uint32 bi = (i < bn) ? b[i] : 0 ;
    register uint32 ci = ai - bi - carry ;
    carry = (carry || bi) && (ci > ai) ;
    c[i] = ci ;
  }
  return carry ? (errno = EOVERFLOW, 0) : 1 ;
}