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#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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}