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mp3: hard-code dithering to 16 bits

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The dithering function audio_linear_dither() worked for signed 16 bits
only anyway, having a variable "bits" just disables important gcc
optimizations.
This commit is contained in:
Max Kellermann 2008-10-10 16:34:52 +02:00
parent 5de7521900
commit bac136608d
1 changed files with 6 additions and 8 deletions
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14
src/inputPlugins/mp3_plugin.c
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@ -65,13 +65,14 @@ static unsigned long prng(unsigned long state)
return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL; return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL;
} }
static int16_t audio_linear_dither(unsigned int bits, mad_fixed_t sample, static int16_t audio_linear_dither(mad_fixed_t sample,
struct audio_dither *dither) struct audio_dither *dither)
{ {
unsigned int scalebits;
mad_fixed_t output, mask, rnd; mad_fixed_t output, mask, rnd;
enum { enum {
bits = 16,
scalebits = MAD_F_FRACBITS + 1 - bits,
MIN = -MAD_F_ONE, MIN = -MAD_F_ONE,
MAX = MAD_F_ONE - 1 MAX = MAD_F_ONE - 1
}; };
@ -83,7 +84,6 @@ static int16_t audio_linear_dither(unsigned int bits, mad_fixed_t sample,
output = sample + (1L << (MAD_F_FRACBITS + 1 - bits - 1)); output = sample + (1L << (MAD_F_FRACBITS + 1 - bits - 1));
scalebits = MAD_F_FRACBITS + 1 - bits;
mask = (1L << scalebits) - 1; mask = (1L << scalebits) - 1;
rnd = prng(dither->random); rnd = prng(dither->random);
@ -119,13 +119,11 @@ static unsigned dither_buffer(int16_t *dest0, const struct mad_synth *synth,
unsigned int i; unsigned int i;
for (i = start; i < end; ++i) { for (i = start; i < end; ++i) {
*dest++ = audio_linear_dither(16, *dest++ = audio_linear_dither(synth->pcm.samples[0][i],
synth->pcm.samples[0][i],
dither); dither);
if (num_channels == 2) if (num_channels == 2)
*dest++ = audio_linear_dither(16, *dest++ = audio_linear_dither(synth->pcm.samples[1][i],
synth->pcm.samples[1][i],
dither); dither);
} }