a

libmp/mpvecdigmuladd.c

@@ -0,0 +1,103 @@
+#include "os.h"
+#include <mp.h>
+#include "dat.h"
+
+#define LO(x) ((x) & ((1<<(Dbits/2))-1))
+#define HI(x) ((x) >> (Dbits/2))
+
+static void
+mpdigmul(mpdigit a, mpdigit b, mpdigit *p)
+{
+	mpdigit x, ah, al, bh, bl, p1, p2, p3, p4;
+	int carry;
+
+	// half digits
+	ah = HI(a);
+	al = LO(a);
+	bh = HI(b);
+	bl = LO(b);
+
+	// partial products
+	p1 = ah*bl;
+	p2 = bh*al;
+	p3 = bl*al;
+	p4 = ah*bh;
+
+	// p = ((p1+p2)<<(Dbits/2)) + (p4<<Dbits) + p3
+	carry = 0;
+	x = p1<<(Dbits/2);
+	p3 += x;
+	if(p3 < x)
+		carry++;
+	x = p2<<(Dbits/2);
+	p3 += x;
+	if(p3 < x)
+		carry++;
+	p4 += carry + HI(p1) + HI(p2);	// can't carry out of the high digit
+	p[0] = p3;
+	p[1] = p4;
+}
+
+// prereq: p must have room for n+1 digits
+void
+mpvecdigmuladd(mpdigit *b, int n, mpdigit m, mpdigit *p)
+{
+	int i;
+	mpdigit carry, x, y, part[2];
+
+	carry = 0;
+	part[1] = 0;
+	for(i = 0; i < n; i++){
+		x = part[1] + carry;
+		if(x < carry)
+			carry = 1;
+		else
+			carry = 0;
+		y = *p;
+		mpdigmul(*b++, m, part);
+		x += part[0];
+		if(x < part[0])
+			carry++;
+		x += y;
+		if(x < y)
+			carry++;
+		*p++ = x;
+	}
+	*p = part[1] + carry;
+}
+
+// prereq: p must have room for n+1 digits
+int
+mpvecdigmulsub(mpdigit *b, int n, mpdigit m, mpdigit *p)
+{
+	int i;
+	mpdigit x, y, part[2], borrow;
+
+	borrow = 0;
+	part[1] = 0;
+	for(i = 0; i < n; i++){
+		x = *p;
+		y = x - borrow;
+		if(y > x)
+			borrow = 1;
+		else
+			borrow = 0;
+		x = part[1];
+		mpdigmul(*b++, m, part);
+		x += part[0];
+		if(x < part[0])
+			borrow++;
+		x = y - x;
+		if(x > y)
+			borrow++;
+		*p++ = x;
+	}
+
+	x = *p;
+	y = x - borrow - part[1];
+	*p = y;
+	if(y > x)
+		return -1;
+	else
+		return 1;
+}