58 lines
879 B
C
58 lines
879 B
C
#include "os.h"
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#include <mp.h>
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#include "dat.h"
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// convert an mpint into a big endian byte array (most significant byte first)
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// return number of bytes converted
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// if p == nil, allocate and result array
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int
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mptobe(mpint *b, uchar *p, uint n, uchar **pp)
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{
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int i, j, suppress;
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mpdigit x;
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uchar *e, *s, c;
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if(p == nil){
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n = (b->top+1)*Dbytes;
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p = malloc(n);
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}
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if(p == nil)
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return -1;
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if(pp != nil)
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*pp = p;
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memset(p, 0, n);
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// special case 0
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if(b->top == 0){
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if(n < 1)
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return -1;
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else
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return 1;
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}
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s = p;
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e = s+n;
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suppress = 1;
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for(i = b->top-1; i >= 0; i--){
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x = b->p[i];
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for(j = Dbits-8; j >= 0; j -= 8){
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c = x>>j;
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if(c == 0 && suppress)
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continue;
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if(p >= e)
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return -1;
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*p++ = c;
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suppress = 0;
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}
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}
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// guarantee at least one byte
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if(s == p){
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if(p >= e)
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return -1;
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*p++ = 0;
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}
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return p - s;
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}
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