Merge commit 'e0b7d30fd437292c88141fb08d60681870b86c6e' as 'subprojects/pixpat'

1 files changed, 62 insertions, 0 deletions

diff --git a/subprojects/pixpat/pixpat-native/src/io/detail.h b/subprojects/pixpat/pixpat-native/src/io/detail.h
new file mode 100644
index 0000000..cb2b9fb
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+++ b/subprojects/pixpat/pixpat-native/src/io/detail.h
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+#pragma once
+
+// Per-component encode/decode against the descriptor + memcpy-based
+// load/store_word helpers. Shared by every Source / Sink template.
+
+#include <cstdint>
+#include <cstring>
+
+#include "../layout.h"
+
+namespace pixpat::detail
+{
+
+// Decode an N-bit stored value into the 16-bit normalized space and
+// encode it back. Decode bit-replicates the stored value across the 16
+// bits so that N-bit max maps to normalized max (e.g. 8-bit 0xFF →
+// 0xFFFF, not 0xFF00). Encode is a plain truncating right-shift: the
+// replicated bits land in the low (16-N) bits and get dropped, so
+// stored→norm→stored is exact for any N in [1, 16].
+//
+// `bits` is taken at runtime; in every call site it traces back to a
+// constexpr Plane::comps[I].bits read, which the optimizer constant-
+// folds after inlining.
+
+constexpr uint16_t decode_norm(unsigned bits, uint16_t stored) noexcept
+{
+	const int N = int(bits);
+	// Loop, not a single OR: one replication only covers 2N bits, so
+	// N < 8 (RGB565, RGBA4444, 1-bit alpha, ...) needs multiple tiles.
+	uint32_t result = 0;
+	for (int s = 16 - N; s > -N; s -= N) {
+		if (s >= 0)
+			result |= uint32_t(stored) << s;
+		else
+			result |= uint32_t(stored) >> -s;
+	}
+	return uint16_t(result);
+}
+
+constexpr uint16_t encode_norm(unsigned bits, uint16_t norm) noexcept
+{
+	return uint16_t(norm >> (16u - bits));
+}
+
+// Read one storage word from `p`. memcpy is uniform for tight and
+// non-tight (e.g. BGR888 24-bit) layouts; the optimizer folds it to a
+// single load when the size is constant.
+template <typename Plane>
+inline typename Plane::storage_t load_word(const uint8_t* p) noexcept
+{
+	typename Plane::storage_t word{};
+	std::memcpy(&word, p, Plane::bytes_per_pixel);
+	return word;
+}
+
+template <typename Plane>
+inline void store_word(uint8_t* p, typename Plane::storage_t word) noexcept
+{
+	std::memcpy(p, &word, Plane::bytes_per_pixel);
+}
+
+} // namespace pixpat::detail