1 // Copyright 2016 Citra Emulator Project
2 // Licensed under GPLv2 or any later version
3 // Refer to the license.txt file included.
4
5 #include <algorithm>
6 #include "audio_core/interpolate.h"
7 #include "common/assert.h"
8
9 namespace AudioCore::AudioInterp {
10
11 // Calculations are done in fixed point with 24 fractional bits.
12 // (This is not verified. This was chosen for minimal error.)
13 constexpr u64 scale_factor = 1 << 24;
14 constexpr u64 scale_mask = scale_factor - 1;
15
16 /// Here we step over the input in steps of rate, until we consume all of the input.
17 /// Three adjacent samples are passed to fn each step.
18 template <typename Function>
StepOverSamples(State & state,StereoBuffer16 & input,float rate,StereoFrame16 & output,std::size_t & outputi,Function fn)19 static void StepOverSamples(State& state, StereoBuffer16& input, float rate, StereoFrame16& output,
20 std::size_t& outputi, Function fn) {
21 ASSERT(rate > 0);
22
23 if (input.empty())
24 return;
25
26 input.insert(input.begin(), {state.xn2, state.xn1});
27
28 const u64 step_size = static_cast<u64>(rate * scale_factor);
29 u64 fposition = state.fposition;
30 std::size_t inputi = 0;
31
32 while (outputi < output.size()) {
33 inputi = static_cast<std::size_t>(fposition / scale_factor);
34
35 if (inputi + 2 >= input.size()) {
36 inputi = input.size() - 2;
37 break;
38 }
39
40 u64 fraction = fposition & scale_mask;
41 output[outputi++] = fn(fraction, input[inputi], input[inputi + 1], input[inputi + 2]);
42
43 fposition += step_size;
44 }
45
46 state.xn2 = input[inputi];
47 state.xn1 = input[inputi + 1];
48 state.fposition = fposition - inputi * scale_factor;
49
50 input.erase(input.begin(), std::next(input.begin(), inputi + 2));
51 }
52
None(State & state,StereoBuffer16 & input,float rate,StereoFrame16 & output,std::size_t & outputi)53 void None(State& state, StereoBuffer16& input, float rate, StereoFrame16& output,
54 std::size_t& outputi) {
55 StepOverSamples(
56 state, input, rate, output, outputi,
57 [](u64 fraction, const auto& x0, const auto& x1, const auto& x2) { return x0; });
58 }
59
Linear(State & state,StereoBuffer16 & input,float rate,StereoFrame16 & output,std::size_t & outputi)60 void Linear(State& state, StereoBuffer16& input, float rate, StereoFrame16& output,
61 std::size_t& outputi) {
62 // Note on accuracy: Some values that this produces are +/- 1 from the actual firmware.
63 StepOverSamples(state, input, rate, output, outputi,
64 [](u64 fraction, const auto& x0, const auto& x1, const auto& x2) {
65 // This is a saturated subtraction. (Verified by black-box fuzzing.)
66 s64 delta0 = std::clamp<s64>(x1[0] - x0[0], -32768, 32767);
67 s64 delta1 = std::clamp<s64>(x1[1] - x0[1], -32768, 32767);
68
69 return std::array<s16, 2>{
70 static_cast<s16>(x0[0] + fraction * delta0 / scale_factor),
71 static_cast<s16>(x0[1] + fraction * delta1 / scale_factor),
72 };
73 });
74 }
75
76 } // namespace AudioCore::AudioInterp
77