From: Andre Noll <maan@systemlinux.org>
Date: Sun, 19 Jul 2009 15:56:22 +0000 (+0200)
Subject: Micro optimizations for the amp filter.
X-Git-Tag: v0.4.0~50^2~2
X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=commitdiff_plain;h=36d1c3d162c687cd11c05e88a93fa1de78f06eab

Micro optimizations for the amp filter.

Use memcpy in the special case amp==0 (no amplification) and optimize the code in
the performance-critical loop. Intrestingly, using the likely()/unlikely() macros made the
code slower.

Results (three runs on identical input data on a 32bit x86 machine under Linux, gcc-4.4.0):

old with --amp 3:
        0m0.776s 0m0.790s 0m0.812s, avg: 792
new with --amp 3:
        0m0.456s 0m0.492s 0m0.477s, avg: 475
speedup: 1.67

old with --amp 0:
        0m0.791s 0m0.808s 0m0.810s, avg: 803
new with --amp 0:
        0m0.100s 0m0.103s 0m0.094s, avg: 99
speedup: 8.1
---

diff --git a/amp_filter.c b/amp_filter.c
index 63b1b9a6..e180db43 100644
--- a/amp_filter.c
+++ b/amp_filter.c
@@ -32,19 +32,29 @@ struct private_amp_data {
 
 static ssize_t amp_convert(char *inbuf, size_t inbuf_len, struct filter_node *fn)
 {
-	size_t i, length = PARA_MIN((inbuf_len / 2) * 2,
-		(fn->bufsize - fn->loaded) / 2 * 2);
+	size_t i, length = PARA_MIN((inbuf_len / 2),
+		(fn->bufsize - fn->loaded) / 2);
 	struct private_amp_data *pad = fn->private_data;
 	int16_t *ip = (int16_t *)inbuf, *op = (int16_t *)(fn->buf + fn->loaded);
+	int factor = 64 + pad->amp;
 
 	if (!length)
 		return 0;
-	for (i = 0; i < length / 2; i++) {
-		int x = (PARA_ABS(*ip) * (64 + pad->amp)) >> 6;
-		*op++ = *ip++ > 0? PARA_MIN(x, 32767) : PARA_MAX(-x, -32768);
+
+	if (pad->amp == 0) {
+		memcpy(op, ip, length * 2);
+		goto out;
+	}
+	for (i = 0; i < length; i++) {
+		int x = (ip[i] * factor) >> 6;
+
+		op[i] = x;
+		if (op[i] != x)
+			op[i] = (x >= 32768)? 32767 : -32768;
 	}
-	fn->loaded += length;
-	return length;
+out:
+	fn->loaded += length * 2;
+	return length * 2;
 }
 
 static void amp_close(struct filter_node *fn)