1 /*
2 * SampleFormatBRR.cpp
3 * -------------------
4 * Purpose: BRR (SNES Bit Rate Reduction) sample format import.
5 * Notes : This format has no magic bytes, so frame headers are thoroughly validated.
6 * Authors: OpenMPT Devs
7 * The OpenMPT source code is released under the BSD license. Read LICENSE for more details.
8 */
9
10
11 #include "stdafx.h"
12 #include "Sndfile.h"
13 #include "../common/FileReader.h"
14
15
16 OPENMPT_NAMESPACE_BEGIN
17
18
ProcessBRRSample(int32 sample,int16 * output,uint8 range,uint8 filter)19 static void ProcessBRRSample(int32 sample, int16 *output, uint8 range, uint8 filter)
20 {
21 if(sample >= 8)
22 sample -= 16;
23
24 if(range <= 12)
25 sample = mpt::rshift_signed(mpt::lshift_signed(sample, range), 1);
26 else
27 sample = (sample < 0) ? -2048 : 0; // Implementations do not fully agree on what to do in this case. This is what bsnes does.
28
29 // Apply prediction filter
30 // Note 1: It is okay that we may access data before the first sample point because this memory is reserved for interpolation
31 // Note 2: The use of signed shift arithmetic is crucial for some samples (e.g. killer lead.brr, Mac2.brr)
32 // Note 3: Divisors are twice of what is written in the respective comments, as all sample data is divided by 2 (again crucial for accuracy)
33 static_assert(InterpolationLookaheadBufferSize >= 2);
34 switch(filter)
35 {
36 case 1: // y(n) = x(n) + x(n-1) * 15/16
37 sample += mpt::rshift_signed(output[-1] * 15, 5);
38 break;
39 case 2: // y(n) = x(n) + x(n-1) * 61/32 - x(n-2) * 15/16
40 sample += mpt::rshift_signed(output[-1] * 61, 6) + mpt::rshift_signed(output[-2] * -15, 5);
41 break;
42 case 3: // y(n) = x(n) + x(n-1) * 115/64 - x(n-2) * 13/16
43 sample += mpt::rshift_signed(output[-1] * 115, 7) + mpt::rshift_signed(output[-2] * -13, 5);
44 break;
45 }
46
47 sample = std::clamp(sample, int32(-32768), int32(32767)) * 2;
48 if(sample > 32767)
49 sample -= 65536;
50 else if(sample < -32768)
51 sample += 65536;
52 output[0] = static_cast<int16>(sample);
53 }
54
55
ReadBRRSample(SAMPLEINDEX sample,FileReader & file)56 bool CSoundFile::ReadBRRSample(SAMPLEINDEX sample, FileReader &file)
57 {
58 const auto fileSize = file.GetLength();
59 if(fileSize < 9 || fileSize > uint16_max)
60 return false;
61 const bool hasLoopInfo = (fileSize % 9) == 2;
62 if((fileSize % 9) != 0 && !hasLoopInfo)
63 return false;
64
65 file.Rewind();
66
67 SmpLength loopStart = 0;
68 if(hasLoopInfo)
69 {
70 loopStart = file.ReadUint16LE();
71 if(loopStart >= fileSize)
72 return false;
73 if((loopStart % 9) != 0)
74 return false;
75 }
76
77 // First scan the file for validity and consistency
78 // Note: There are some files with loop start set but ultimately the loop is never enabled. Cannot use this as a consistency check.
79 // Very few files also have a filter set on the first block, so we cannot reject those either.
80 bool enableLoop = false, first = true;
81 while(!file.EndOfFile())
82 {
83 const auto block = file.ReadArray<uint8, 9>();
84 const bool isLast = (block[0] & 0x01) != 0;
85 const bool isLoop = (block[0] & 0x02) != 0;
86 const uint8 range = block[0] >> 4u;
87 if(isLast != file.EndOfFile())
88 return false;
89 if(!first && enableLoop != isLoop)
90 return false;
91 // While a range of 13 is technically invalid as well, it can be found in the wild.
92 if(range > 13)
93 return false;
94 enableLoop = isLoop;
95 first = false;
96 }
97
98 file.Seek(hasLoopInfo ? 2 : 0);
99
100 DestroySampleThreadsafe(sample);
101 ModSample &mptSmp = Samples[sample];
102 mptSmp.Initialize();
103 mptSmp.uFlags = CHN_16BIT;
104 mptSmp.nLength = mpt::saturate_cast<SmpLength>((fileSize - (hasLoopInfo ? 2 : 0)) * 16 / 9);
105 if(enableLoop)
106 mptSmp.SetLoop(loopStart * 16 / 9, mptSmp.nLength, true, false, *this);
107 mptSmp.nC5Speed = 32000;
108 m_szNames[sample] = "";
109
110 if(!mptSmp.AllocateSample())
111 return false;
112
113 int16 *output = mptSmp.sample16();
114 while(!file.EndOfFile())
115 {
116 const auto block = file.ReadArray<uint8, 9>();
117 const uint8 range = block[0] >> 4u;
118 const uint8 filter = (block[0] >> 2) & 0x03;
119
120 for(int i = 0; i < 8; i++)
121 {
122 ProcessBRRSample(block[i + 1] >> 4u, output, range, filter);
123 ProcessBRRSample(block[i + 1] & 0x0F, output + 1, range, filter);
124 output += 2;
125 }
126 }
127 mptSmp.Convert(MOD_TYPE_IT, GetType());
128 mptSmp.PrecomputeLoops(*this, false);
129
130 return true;
131 }
132
133
134 OPENMPT_NAMESPACE_END
135