tomsfastmath/src/bin/fp_read_unsigned_bin.c
2010-07-22 10:06:30 +02:00

67 lines
1.6 KiB
C

/* TomsFastMath, a fast ISO C bignum library.
*
* This project is meant to fill in where LibTomMath
* falls short. That is speed ;-)
*
* This project is public domain and free for all purposes.
*
* Tom St Denis, tomstdenis@gmail.com
*/
#include <tfm.h>
void fp_read_unsigned_bin(fp_int *a, unsigned char *b, int c)
{
/* zero the int */
fp_zero (a);
/* If we know the endianness of this architecture, and we're using
32-bit fp_digits, we can optimize this */
#if (defined(ENDIAN_LITTLE) || defined(ENDIAN_BIG)) && !defined(FP_64BIT)
/* But not for both simultaneously */
#if defined(ENDIAN_LITTLE) && defined(ENDIAN_BIG)
#error Both ENDIAN_LITTLE and ENDIAN_BIG defined.
#endif
{
unsigned char *pd = (unsigned char *)a->dp;
if ((unsigned)c > (FP_SIZE * sizeof(fp_digit))) {
int excess = c - (FP_SIZE * sizeof(fp_digit));
c -= excess;
b += excess;
}
a->used = (c + sizeof(fp_digit) - 1)/sizeof(fp_digit);
/* read the bytes in */
#ifdef ENDIAN_BIG
{
/* Use Duff's device to unroll the loop. */
int idx = (c - 1) & ~3;
switch (c % 4) {
case 0: do { pd[idx+0] = *b++;
case 3: pd[idx+1] = *b++;
case 2: pd[idx+2] = *b++;
case 1: pd[idx+3] = *b++;
idx -= 4;
} while ((c -= 4) > 0);
}
}
#else
for (c -= 1; c >= 0; c -= 1) {
pd[c] = *b++;
}
#endif
}
#else
/* read the bytes in */
for (; c > 0; c--) {
fp_mul_2d (a, 8, a);
a->dp[0] |= *b++;
a->used += 1;
}
#endif
fp_clamp (a);
}
/* $Source$ */
/* $Revision$ */
/* $Date$ */