Optimise zpow and zmodpow

Signed-off-by: Mattias Andrée <maandree@kth.se>

1 files changed, 10 insertions, 5 deletions

diff --git a/src/zpow.c b/src/zpow.c
index bc071f8..c359ac3 100644
--- a/src/zpow.c
+++ b/src/zpow.c
@@ -10,7 +10,8 @@
 void
 zpow(z_t a, z_t b, z_t c)
 {
-	size_t i, n;
+	size_t i, j, n, bits;
+	zahl_char_t x;
 
 	if (zsignum(c) <= 0) {
 		if (zzero(c)) {
@@ -31,15 +32,19 @@ zpow(z_t a, z_t b, z_t c)
 		return;
 	}
 
-	n = zbits(c);
+	bits = zbits(c);
+	n = FLOOR_BITS_TO_CHARS(bits);
 
 	zset(tb, b);
 	zset(tc, c);
 	zsetu(a, 1);
 
 	for (i = 0; i < n; i++) {
-		if (zbtest(tc, i))
-			zmul(a, a, tb);
-		zsqr(tb, tb);
+		x = tc->chars[i];
+		for (j = BITS_PER_CHAR; j--; x >>= 1, j) {
+			if (x & 1)
+				zmul(a, a, tb);
+			zsqr(tb, tb);
+		}
 	}
 }