mirrors/pipewire
1
0
Fork 0
mirror of https://gitlab.freedesktop.org/pipewire/pipewire.git synced 2025-11-05 13:30:02 -05:00
Code Issues Projects Releases Packages Wiki Activity Actions

audioconvert: avoid even more precision loss in S32 to F32 conversion

Browse source 
There's really no point in doing that s25_32 intermediate step,
to be honest i don't have a clue why the original implementation
did that \_(ツ)_/¯.

Both `S25_SCALE` and `S32_SCALE` are powers of two,
and thus are both exactly representable as floats,
and reprocial of power-of-two is also exactly representable,
so it's not like that rescaling results in precision loss.

This additionally avoids right-shift, and thus is even faster.

As `test_lossless_s32_lossless_subset` shows,
if the integer is in the form of s25+shift,
the maximal absolute error became even lower,
but not zero, because F32->S32 still goes through S25 intermediate.
I think we could theoretically do better,
but then the clamping becomes pretty finicky,
so i don't feel like touching that here.
This commit is contained in:
Roman Lebedev 2024-06-14 06:05:18 +03:00
parent c517865864
commit f4c89b1b40
No known key found for this signature in database
GPG key ID: 083C3EBB4A1689E0
4 changed files with 26 additions and 37 deletions
Download patch file Download diff file Expand all files Collapse all files

14
spa/plugins/audioconvert/test-fmt-ops.c
View file

@ -336,7 +336,7 @@ static void test_s32_f32(void)
0xFFFFFF00, 0x0200, 0xFFFFFE00
};
static const float out[] = { 0.e+00f, 9.99999940395355224609375e-01f, -1.e+00f,
static const float out[] = { 0.e+00f, 1.e+00f, -1.e+00f,
9.9999988079071044921875e-01f, -9.9999988079071044921875e-01f, 5.e-01f,
-5.e-01f, 5.9604644775390625e-08f, -5.9604644775390625e-08f,
1.1920928955078125e-07f, -1.1920928955078125e-07f,
@ -672,15 +672,15 @@ static void test_lossless_s32(void)
{
int64_t i;
int32_t max_abs_err = -1;
const int32_t expected_max_abs_err = 127;
fprintf(stderr, "test %s:\n", __func__);
for (i = S32_MIN; i < S32_MAX; i += (expected_max_abs_err >> 1)) {
for (i = S32_MIN; i < S32_MAX; i += 63) {
float v = S32_TO_F32(i);
int32_t t = F32_TO_S32(v);
max_abs_err = SPA_MAX(max_abs_err, SPA_ABS(i - t));
spa_assert_se(SPA_ABS(i - t) <= 126);
// NOTE: 126 is the maximal absolute error given step=1,
// for wider steps it may (errneously) be lower,
// because we may not check some integer that would bump it.
}
spa_assert_se(max_abs_err == expected_max_abs_err);
}
static void test_lossless_s32_lossless_subset(void)
@ -700,7 +700,7 @@ static void test_lossless_s32_lossless_subset(void)
}
}
spa_assert_se(!all_lossless);
spa_assert_se(max_abs_err == 127);
spa_assert_se(max_abs_err == 64);
}
static void test_lossless_u32(void)