From: Eric Biggers <ebiggers3@gmail.com>
Date: Mon, 20 Jul 2015 04:13:53 +0000 (-0500)
Subject: Avoid branch in 'num_bits == 0' branch when peeking bits
X-Git-Tag: v1.8.2~41
X-Git-Url: https://wimlib.net/git/?p=wimlib;a=commitdiff_plain;h=9bb97aee4a44801c1d755916aa7a132b2cdec80f

Avoid branch in 'num_bits == 0' branch when peeking bits
---

diff --git a/include/wimlib/decompress_common.h b/include/wimlib/decompress_common.h
index 420f7f41..ce731dca 100644
--- a/include/wimlib/decompress_common.h
+++ b/include/wimlib/decompress_common.h
@@ -90,9 +90,7 @@ overflow:
 static inline u32
 bitstream_peek_bits(const struct input_bitstream *is, const unsigned num_bits)
 {
-	if (unlikely(num_bits == 0))
-		return 0;
-	return is->bitbuf >> (32 - num_bits);
+	return (is->bitbuf >> 1) >> (sizeof(is->bitbuf) * 8 - num_bits - 1);
 }
 
 /* Remove @num_bits from the bitstream.  There must be at least @num_bits
diff --git a/src/lzms_decompress.c b/src/lzms_decompress.c
index 7f82803c..bd7e76e1 100644
--- a/src/lzms_decompress.c
+++ b/src/lzms_decompress.c
@@ -430,9 +430,7 @@ lzms_ensure_bits(struct lzms_input_bitstream *is, unsigned num_bits)
 static inline bitbuf_t
 lzms_peek_bits(struct lzms_input_bitstream *is, unsigned num_bits)
 {
-	if (unlikely(num_bits == 0))
-		return 0;
-	return is->bitbuf >> (sizeof(is->bitbuf) * 8 - num_bits);
+	return (is->bitbuf >> 1) >> (sizeof(is->bitbuf) * 8 - num_bits - 1);
 }
 
 /* Remove @num_bits bits from the bitbuffer variable.  */