a

libmp/mptobe.c

@@ -0,0 +1,57 @@
+#include "os.h"
+#include <mp.h>
+#include "dat.h"
+
+// convert an mpint into a big endian byte array (most significant byte first)
+//   return number of bytes converted
+//   if p == nil, allocate and result array
+int
+mptobe(mpint *b, uchar *p, uint n, uchar **pp)
+{
+	int i, j, suppress;
+	mpdigit x;
+	uchar *e, *s, c;
+
+	if(p == nil){
+		n = (b->top+1)*Dbytes;
+		p = malloc(n);
+	}
+	if(p == nil)
+		return -1;
+	if(pp != nil)
+		*pp = p;
+	memset(p, 0, n);
+
+	// special case 0
+	if(b->top == 0){
+		if(n < 1)
+			return -1;
+		else
+			return 1;
+	}
+		
+	s = p;
+	e = s+n;
+	suppress = 1;
+	for(i = b->top-1; i >= 0; i--){
+		x = b->p[i];
+		for(j = Dbits-8; j >= 0; j -= 8){
+			c = x>>j;
+			if(c == 0 && suppress)
+				continue;
+			if(p >= e)
+				return -1;
+			*p++ = c;
+			suppress = 0;
+		}
+	}
+
+	// guarantee at least one byte
+	if(s == p){
+		if(p >= e)
+			return -1;
+		*p++ = 0;
+	}
+
+	return p - s;
+}