a

libmp/betomp.c

@@ -0,0 +1,40 @@
+#include "os.h"
+#include <mp.h>
+#include "dat.h"
+
+// convert a big-endian byte array (most significant byte first) to an mpint
+mpint*
+betomp(uchar *p, uint n, mpint *b)
+{
+	int m, s;
+	mpdigit x;
+
+	if(b == nil)
+		b = mpnew(0);
+
+	// dump leading zeros
+	while(*p == 0 && n > 1){
+		p++;
+		n--;
+	}
+
+	// get the space
+	mpbits(b, n*8);
+	b->top = DIGITS(n*8);
+	m = b->top-1;
+
+	// first digit might not be Dbytes long
+	s = ((n-1)*8)%Dbits;
+	x = 0;
+	for(; n > 0; n--){
+		x |= ((mpdigit)(*p++)) << s;
+		s -= 8;
+		if(s < 0){
+			b->p[m--] = x;
+			s = Dbits-8;
+			x = 0;
+		}
+	}
+
+	return b;
+}