From 327747de15be919f8060e12a2e82afa37500629f Mon Sep 17 00:00:00 2001
From: Justin Ruggles <justin.ruggles@gmail.com>
Date: Thu, 18 Oct 2012 23:11:20 -0400
Subject: [PATCH] atrac3: simplify MDCT window calculation
---
libavcodec/atrac3.c | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)
diff --git a/libavcodec/atrac3.c b/libavcodec/atrac3.c
index 9e0f27332e3..76e251ba1cc 100644
--- a/libavcodec/atrac3.c
+++ b/libavcodec/atrac3.c
@@ -177,19 +177,16 @@ static int decode_bytes(const uint8_t *input, uint8_t *out, int bytes)
static av_cold void init_atrac3_window(void)
{
- float enc_window[256];
- int i;
+ int i, j;
/* generate the mdct window, for details see
* http://wiki.multimedia.cx/index.php?title=RealAudio_atrc#Windows */
- for (i = 0; i < 256; i++)
- enc_window[i] = (sin(((i + 0.5) / 256.0 - 0.5) * M_PI) + 1.0) * 0.5;
-
- for (i = 0; i < 256; i++) {
- mdct_window[i] = enc_window[i] /
- (enc_window[ i] * enc_window[ i] +
- enc_window[255 - i] * enc_window[255 - i]);
- mdct_window[511 - i] = mdct_window[i];
+ for (i = 0, j = 255; i < 128; i++, j--) {
+ float wi = sin(((i + 0.5) / 256.0 - 0.5) * M_PI) + 1.0;
+ float wj = sin(((j + 0.5) / 256.0 - 0.5) * M_PI) + 1.0;
+ float w = 0.5 * (wi * wi + wj * wj);
+ mdct_window[i] = mdct_window[511 - i] = wi / w;
+ mdct_window[j] = mdct_window[511 - j] = wj / w;
}
}
--
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