Add dither when requantising >16 bit samples

1 files changed, 25 insertions, 0 deletions

diff --git a/src/codecs/sample.cpp b/src/codecs/sample.cpp
new file mode 100644
index 00000000..c5c96fb9
--- /dev/null
+++ b/src/codecs/sample.cpp
@@ -0,0 +1,25 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include "sample.hpp"
+
+#include <cstdint>
+
+#include "komihash.h"
+
+namespace sample {
+
+static uint64_t sSeed1{0};
+static uint64_t sSeed2{0};
+
+auto applyDither(int64_t src, uint_fast8_t bits) -> int32_t {
+  uint64_t mask = 0xFFFFFFFF;                          // 32 ones
+  mask >>= 32 - bits;                                  // `bits` ones
+  uint64_t noise = komirand(&sSeed1, &sSeed2) & mask;  // `bits` random noise
+  return std::clamp<int64_t>(src + noise, INT32_MIN, INT32_MAX);
+}
+
+}  // namespace sample