a

libmp/mprand.c

@@ -0,0 +1,42 @@
+#include "os.h"
+#include <mp.h>
+#include <libsec.h>
+#include "dat.h"
+
+mpint*
+mprand(int bits, void (*gen)(uchar*, int), mpint *b)
+{
+	int n, m;
+	mpdigit mask;
+	uchar *p;
+
+	n = DIGITS(bits);
+	if(b == nil)
+		b = mpnew(bits);
+	else
+		mpbits(b, bits);
+
+	p = malloc(n*Dbytes);
+	if(p == nil)
+		return nil;
+	(*gen)(p, n*Dbytes);
+	betomp(p, n*Dbytes, b);
+	free(p);
+
+	// make sure we don't give too many bits
+	m = bits%Dbits;
+	n--;
+	if(m > 0){
+		mask = 1;
+		mask <<= m;
+		mask--;
+		b->p[n] &= mask;
+	}
+
+	for(; n >= 0; n--)
+		if(b->p[n] != 0)
+			break;
+	b->top = n+1;
+	b->sign = 1;
+	return b;
+}