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Rewrite the linear sample rate conversion algorithm to make it less hacky and to support arbitrarly big ratios

This commit is contained in:
Pierre Bourdon 2012-12-18 17:38:41 +01:00
parent 1cecbaedce
commit 2c10ca4e46
1 changed files with 21 additions and 39 deletions
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60
Source/Core/Core/Src/HW/DSPHLE/UCodes/UCode_AX_Voice.h
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@ -256,56 +256,38 @@ void GetInputSamples(PB_TYPE& pb, s16* samples)
// samples.
u32 curr_pos = pb.src.cur_addr_frac;
// Compute the number of real samples we will need to read from the
// data source. We need to output 32 samples, so we need to read
// 32 * ratio + curr_pos samples. There does not seem to be a maximum
// value for the ratio in recent versions of AXWii (previously it was
// limited to 4.0), so we will limit it to 16.0 and clamp the ratio if
// needed. This is a HACK, and using another algorithm for linear
// interpolation might be a better idea.
if (ratio > 0x00100000)
ratio = 0x00100000;
s16 real_samples[514];
u32 real_samples_needed = (32 * ratio + curr_pos) >> 16;
// The first two real samples are the ones we read at the previous
// iteration. That way we can interpolate before having read 2 new
// samples from the accelerator.
//
// The next real samples are read from the accelerator.
real_samples[0] = pb.src.last_samples[2];
real_samples[1] = pb.src.last_samples[3];
for (u32 i = 0; i < real_samples_needed; ++i)
real_samples[i + 2] = AcceleratorGetSample();
// These are the two samples between which we interpolate. The initial
// values are stored in the PB, and we update them when resampling the
// input data.
s16 curr0 = pb.src.last_samples[2];
s16 curr1 = pb.src.last_samples[3];
for (u32 i = 0; i < 32; ++i)
{
// Get our current integer and fractional position. The integer
// position is used to get the two samples around us. The
// fractional position is used to compute the linear interpolation
// between these two samples.
u32 curr_int_pos = (curr_pos >> 16);
// Get our current fractional position, used to know how much of
// curr0 and how much of curr1 the output sample should be.
s32 curr_frac_pos = curr_pos & 0xFFFF;
s16 samp1 = real_samples[curr_int_pos];
s16 samp2 = real_samples[curr_int_pos + 1];
// Linear interpolation: s1 + (s2 - s1) * pos
s16 sample = samp1 + (s16)(((samp2 - samp1) * (s32)curr_frac_pos) >> 16);
s16 sample = curr0 + (s16)(((curr1 - curr0) * (s32)curr_frac_pos) >> 16);
samples[i] = sample;
curr_pos += ratio;
// While our current position is >= 1.0, shift to the next 2
// samples for interpolation.
while ((curr_pos >> 16) != 0)
{
curr0 = curr1;
curr1 = AcceleratorGetSample();
curr_pos -= 0x10000;
}
}
// Update the last_samples array. A bit tricky because we can't know
// for sure we have more than 4 real samples in our array.
if (real_samples_needed >= 2)
memcpy(pb.src.last_samples, &real_samples[real_samples_needed + 2 - 4], 4 * sizeof (u16));
else
{
memmove(pb.src.last_samples, &pb.src.last_samples[real_samples_needed], (4 - real_samples_needed) * sizeof (u16));
memcpy(&pb.src.last_samples[4 - real_samples_needed], &real_samples[2], real_samples_needed * sizeof (u16));
}
// Update the two last_samples values in the PB as well as the current
// position.
pb.src.last_samples[2] = curr0;
pb.src.last_samples[3] = curr1;
pb.src.cur_addr_frac = curr_pos & 0xFFFF;
}
else // SRCTYPE_NEAREST