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wmapro: add a two-channel path to the channel transform

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inverse_channel_transform() ran its general N-channel matrix loop
for every sample of a stereo stream, where the matrix is exactly
+-1.0. That loop was a quarter to a third of the whole decode, and
GCC 9.5.0 compiles it worse than 4.9.4 did, which made the codec
6-9% slower on ARM7TDMI after the toolchain update.

Handle a group of two channels separately: add and subtract when
the matrix is +-1.0, and a plain four multiply loop otherwise. More
than two channels still use the general loop.

This reverses the regression from the GCC 9.5.0 update and goes
well past it. The loop the newer compiler handled badly is no longer
used for stereo, so the two compilers now give the same speed to
within 1%, about 25% faster than the codec was with GCC 4.9.4
(estimated with perfsim, e200v1, wmapro_141k: 25.81 MHz with 4.9.4
before this change, 19.5 MHz with either compiler after it).

Output is bit-identical: whole-file PCM hashes match before and
after for five stereo files at 55-271 kbps, built with GCC 9.5.0
and with 4.9.4, and also with the multiply path forced on.

Measured with test_codec, wmapro_141k.wma, MHz for real time:

  Sansa e200v1  27.99 -> 19.70
  Sansa Clip+   21.78 -> 15.80

Estimated with perfsim for the other files (e200v1 / Clip+):

  wmapro_55k   25.21 -> 17.06 / 20.02 -> 13.71
  wmapro_80k   26.17 -> 18.01 / 20.75 -> 14.44
  wmapro_173k  28.52 -> 20.29 / 22.55 -> 16.25
  wmapro_271k  30.85 -> 22.52 / 24.34 -> 18.04

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Michael Giacomelli 2026-10-05 14:36:12 -04:00
parent 361913fdd2
commit 4502948cd8
1 changed files with 55 additions and 14 deletions
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69
lib/rbcodec/codecs/libwmapro/wmaprodec.c
View file

@ -1030,6 +1030,38 @@ static int decode_scale_factors(WMAProDecodeCtx* s)
return 0;
}
/**
*@brief Apply a 2x2 decorrelation matrix to one band of two channels.
* Two channels are by far the common case; the results are the
* same as the general loop's in inverse_channel_transform().
*@param ch0 first channel's coefficients
*@param ch1 second channel's coefficients
*@param mat the matrix, as 16.16 fixed point
*@param len number of coefficients
*/
static inline void decorrelate_stereo(int32_t *ch0, int32_t *ch1,
const int32_t *mat, int len)
{
const int32_t m0 = mat[0], m1 = mat[1], m2 = mat[2], m3 = mat[3];
if (m0 == ONE_FRACT16 && m1 == -ONE_FRACT16 &&
m2 == ONE_FRACT16 && m3 == ONE_FRACT16) {
/* The matrix of a stereo stream. Multiplying by +-1.0 is exact,
* so add and subtract; unsigned, as the multiply's result wraps. */
for (; len > 0; len--) {
uint32_t a = *ch0, b = *ch1;
*ch0++ = a - b;
*ch1++ = a + b;
}
} else {
for (; len > 0; len--) {
int32_t a = *ch0, b = *ch1;
*ch0++ = fixmul16(m0, a) + fixmul16(m1, b);
*ch1++ = fixmul16(m2, a) + fixmul16(m3, b);
}
}
}
/**
*@brief Reconstruct the individual channel data.
*@param s codec context
@ -1052,24 +1084,33 @@ static void inverse_channel_transform(WMAProDecodeCtx *s)
sfb < s->cur_sfb_offsets + s->num_bands; sfb++) {
int y;
if (*tb++ == 1) {
/** multiply values with the decorrelation_matrix */
for (y = sfb[0]; y < FFMIN(sfb[1], s->subframe_len); y++) {
const int32_t* mat = s->chgroup[i].fixdecorrelation_matrix;
const int32_t* data_end = data + num_channels;
int32_t* data_ptr = data;
int32_t** ch;
if (num_channels == 2) {
decorrelate_stereo(ch_data[0] + sfb[0],
ch_data[1] + sfb[0],
s->chgroup[i].fixdecorrelation_matrix,
FFMIN(sfb[1], s->subframe_len) - sfb[0]);
} else {
/** multiply values with the decorrelation_matrix */
for (y = sfb[0];
y < FFMIN(sfb[1], s->subframe_len); y++) {
const int32_t* mat =
s->chgroup[i].fixdecorrelation_matrix;
const int32_t* data_end = data + num_channels;
int32_t* data_ptr = data;
int32_t** ch;
for (ch = ch_data; ch < ch_end; ch++)
*data_ptr++ = (*ch)[y];
for (ch = ch_data; ch < ch_end; ch++)
*data_ptr++ = (*ch)[y];
for (ch = ch_data; ch < ch_end; ch++) {
int32_t sum = 0;
data_ptr = data;
for (ch = ch_data; ch < ch_end; ch++) {
int32_t sum = 0;
data_ptr = data;
while (data_ptr < data_end)
sum += fixmul16(*mat++, *data_ptr++);
while (data_ptr < data_end)
sum += fixmul16(*mat++, *data_ptr++);
(*ch)[y] = sum;
(*ch)[y] = sum;
}
}
}
} else if (s->num_channels == 2) {