Do our own resampling

1 files changed, 59 insertions, 0 deletions

diff --git a/src/codecs/include/sample.hpp b/src/codecs/include/sample.hpp
new file mode 100644
index 00000000..7209673b
--- /dev/null
+++ b/src/codecs/include/sample.hpp
@@ -0,0 +1,59 @@
+#pragma once
+
+#include <stdint.h>
+
+#include <algorithm>
+
+#include <mad.h>
+
+namespace sample {
+
+// A signed, 32-bit PCM sample.
+typedef int32_t Sample;
+
+constexpr auto Clip(int64_t v) -> Sample {
+  if (v > INT32_MAX)
+    return INT32_MAX;
+  if (v < INT32_MIN)
+    return INT32_MIN;
+  return v;
+}
+
+constexpr auto FromSigned(int32_t src, uint_fast8_t bits) -> Sample {
+  // Left-align samples, effectively scaling them up to 32 bits.
+  return src << (sizeof(Sample) * 8 - bits);
+}
+
+constexpr auto FromUnsigned(uint32_t src, uint_fast8_t bits) -> Sample {
+  // Left-align, then substract the max value / 2 to make the sample centred
+  // around zero.
+  return (src << (sizeof(uint32_t) * 8 - bits)) - (~0UL >> 1);
+}
+
+constexpr auto FromFloat(float src) -> Sample {
+  return std::clamp<float>(src, -1.0f, 1.0f) * static_cast<float>(INT32_MAX);
+}
+
+constexpr auto FromDouble(double src) -> Sample {
+  return std::clamp<double>(src, -1.0, 1.0) * static_cast<double>(INT32_MAX);
+}
+
+constexpr auto FromMad(mad_fixed_t src) -> Sample {
+  // Round the bottom bits.
+  src += (1L << (MAD_F_FRACBITS - 24));
+
+  // Clip the leftover bits to within range.
+  if (src >= MAD_F_ONE)
+    src = MAD_F_ONE - 1;
+  else if (src < -MAD_F_ONE)
+    src = -MAD_F_ONE;
+
+  // Quantize.
+  return FromSigned(src >> (MAD_F_FRACBITS + 1 - 24), 24);
+}
+
+constexpr auto ToSigned16Bit(Sample src) -> uint16_t {
+  return src >> 16;
+}
+
+}  // namespace sample