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scalar.c
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scalar.c
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/*
* File: dclxvi-20110718/scalar.c
* Author: Ruben Niederhagen, Peter Schwabe
* Public Domain
*/
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include "scalar.h"
void scalar_setrandom(scalar_t rop, const scalar_t bound)
{
int i;
FILE *urand = fopen("/dev/urandom", "r");
if (urand == NULL) {
fprintf(stderr, "Could not open device file /dev/urandom");
exit(1);
}
do {
for (i = 0; i < 32; i++)
i[(unsigned char *)rop] = fgetc(urand);
}
while (!scalar_le(rop, bound));
fclose(urand);
}
void scalar_set_lluarray(scalar_t rop, unsigned long long v[4])
{
int i;
for (i = 0; i < 4; i++)
rop[i] = v[i];
}
int scalar_getbit(const scalar_t s, unsigned int pos)
{
assert(pos < 256);
return (s[pos >> 6] >> (pos & 0x3f)) & 1;
}
// Returns the position of the most significant set bit
int scalar_scanb(const scalar_t s)
{
int i;
unsigned int pos = 0;
for (i = 255; i > 0; i--)
if (scalar_getbit(s, i) && pos == 0)
pos = i;
return pos;
}
// Returns 1 if a < b, 0 otherwise
int scalar_le(const scalar_t a, const scalar_t b)
{
int r;
r = a[3] < b[3];
if (a[3] == b[3]) {
r = a[2] < b[2];
if (a[2] == b[2]) {
r = a[1] < b[1];
if (a[0] == b[0])
r = a[0] < b[0];
}
}
return r;
}
void scalar_print(FILE * fh, const scalar_t t)
{
int i;
for (i = 3; i >= 0; i--)
fprintf(fh, "%llx", t[i]);
}