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Copy pathg711.cpp
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119 lines (106 loc) · 2.72 KB
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#include "rtp/g711.h"
namespace rtp {
namespace g711 {
// Bias used by the classic μ-law encoder.
constexpr int kUlawBias = 0x84;
constexpr int kUlawClip = 32635;
int16_t UlawToLinear(uint8_t ulaw) {
ulaw = static_cast<uint8_t>(~ulaw);
int t = ((ulaw & 0x0f) << 3) + kUlawBias;
t <<= (static_cast<int>(ulaw & 0x70) >> 4);
return static_cast<int16_t>((ulaw & 0x80) ? (kUlawBias - t) : (t - kUlawBias));
}
uint8_t LinearToUlaw(int16_t pcm) {
int sample = pcm;
int sign = 0;
if (sample < 0) {
sign = 0x80;
sample = -sample;
}
if (sample > kUlawClip) {
sample = kUlawClip;
}
sample += kUlawBias;
int exponent = 7;
for (int exp_mask = 0x4000; (sample & exp_mask) == 0 && exponent > 0;
exp_mask >>= 1) {
--exponent;
}
const int mantissa = (sample >> (exponent + 3)) & 0x0f;
const uint8_t ulaw =
static_cast<uint8_t>(~(sign | (exponent << 4) | mantissa));
return ulaw;
}
int16_t AlawToLinear(uint8_t alaw) {
alaw ^= 0x55;
int t = (alaw & 0x0f) << 4;
const int seg = (alaw & 0x70) >> 4;
switch (seg) {
case 0:
t += 8;
break;
case 1:
t += 0x108;
break;
default:
t += 0x108;
t <<= (seg - 1);
break;
}
return static_cast<int16_t>((alaw & 0x80) ? t : -t);
}
uint8_t LinearToAlaw(int16_t pcm) {
int sample = pcm;
int sign = 0;
if (sample >= 0) {
sign = 0x80;
} else {
sample = -sample - 8;
if (sample < 0) {
sample = 0;
}
}
if (sample > 32635) {
sample = 32635;
}
int exponent = 7;
for (int exp_mask = 0x4000; (sample & exp_mask) == 0 && exponent > 0;
exp_mask >>= 1) {
--exponent;
}
int mantissa;
if (exponent == 0) {
mantissa = sample >> 4;
} else {
mantissa = (sample >> (exponent + 3)) & 0x0f;
}
const uint8_t alaw =
static_cast<uint8_t>(sign | (exponent << 4) | mantissa);
return static_cast<uint8_t>(alaw ^ 0x55);
}
uint8_t UlawToAlaw(uint8_t ulaw) { return LinearToAlaw(UlawToLinear(ulaw)); }
uint8_t AlawToUlaw(uint8_t alaw) { return LinearToUlaw(AlawToLinear(alaw)); }
std::vector<uint8_t> ConvertPayload(const std::vector<uint8_t>& in,
uint8_t in_pt,
uint8_t out_pt) {
if (in_pt == out_pt) {
return in;
}
std::vector<uint8_t> out(in.size());
if (in_pt == kPayloadTypePcmu && out_pt == kPayloadTypePcma) {
for (size_t i = 0; i < in.size(); ++i) {
out[i] = UlawToAlaw(in[i]);
}
return out;
}
if (in_pt == kPayloadTypePcma && out_pt == kPayloadTypePcmu) {
for (size_t i = 0; i < in.size(); ++i) {
out[i] = AlawToUlaw(in[i]);
}
return out;
}
// Unknown mapping: pass through unchanged.
return in;
}
} // namespace g711
} // namespace rtp