drawterm/libmp/mptole.c

55 lines
786 B
C

#include "os.h"
#include <mp.h>
#include "dat.h"
// convert an mpint into a little endian byte array (least significant byte first)
// return number of bytes converted
// if p == nil, allocate and result array
int
mptole(mpint *b, uchar *p, uint n, uchar **pp)
{
int i, j;
mpdigit x;
uchar *e, *s;
if(p == nil){
n = (b->top+1)*Dbytes;
p = malloc(n);
}
if(pp != nil)
*pp = p;
if(p == nil)
return -1;
memset(p, 0, n);
// special case 0
if(b->top == 0){
if(n < 1)
return -1;
else
return 0;
}
s = p;
e = s+n;
for(i = 0; i < b->top-1; i++){
x = b->p[i];
for(j = 0; j < Dbytes; j++){
if(p >= e)
return -1;
*p++ = x;
x >>= 8;
}
}
x = b->p[i];
while(x > 0){
if(p >= e)
return -1;
*p++ = x;
x >>= 8;
}
return p - s;
}