flate

commit 4fcde3912027a729b762b199ba1f0b25209374b2
parent 966429e2a5d9e15ac6ee0a47eb715b8dfd04550f
Author: nsz <nszabolcs@gmail.com>
Date:   Tue, 28 Apr 2009 07:49:58 +0200

faster getbits
Diffstat:
inflate.c
 | 
24
+++++++++++++++++-------

1 file changed, 17 insertions(+), 7 deletions(-)
diff --git a/inflate.c b/inflate.c
@@ -196,7 +196,7 @@ static void init_fixed_huffs(void) {
 	build_huff(&dhuff, lens, Ndist, 5);
 }
 
-/* get one bit from s->src stream */
+/* get one bit from stream */
 static uint getbit(Stream *s) {
 	uint bit;
 
@@ -213,16 +213,26 @@ static uint getbit(Stream *s) {
 	return bit;
 }
 
-/* get n bits from s->src stream */
+/* get n bits from stream */
 static uint getbits(Stream *s, int n) {
-	uint bits = 0;
-	int i;
+	uint bits;
+	uint nbits;
 
 	if (n == 0)
 		return 0;
-	for (i = 0; i < n; i++)
-		bits |= getbit(s) << i;
-	return bits;
+	bits = s->bits;
+	nbits = s->nbits;
+	while (nbits < n) {
+		if (s->src == s->srcend) {
+			s->error = FlateShortSrc;
+			return 0;
+		}
+		bits |= (*s->src++ << nbits);
+		nbits += 8;
+	}
+	s->bits = bits >> n;
+	s->nbits = nbits - n;
+	return bits & ((1 << n) - 1);
 }
 
 /* decode a symbol from stream with tree */