Move memcpy_interleaved into its own file.

[nageru] / memcpy_interleaved.cpp

diff --git a/memcpy_interleaved.cpp b/memcpy_interleaved.cpp
new file mode 100644 (file)
index 0000000..9a41cdd
--- /dev/null
+++ b/memcpy_interleaved.cpp
@@ -0,0 +1,136 @@
+#include <cstdint>
+#include <algorithm>
+#include <assert.h>
+#if __SSE2__
+#include <immintrin.h>
+#endif
+
+using namespace std;
+
+// TODO: Support stride.
+void memcpy_interleaved_slow(uint8_t *dest1, uint8_t *dest2, const uint8_t *src, size_t n)
+{
+       assert(n % 2 == 0);
+       uint8_t *dptr1 = dest1;
+       uint8_t *dptr2 = dest2;
+
+       for (size_t i = 0; i < n; i += 2) {
+               *dptr1++ = *src++;
+               *dptr2++ = *src++;
+       }
+}
+
+#ifdef __SSE2__
+
+// Returns the number of bytes consumed.
+size_t memcpy_interleaved_fastpath(uint8_t *dest1, uint8_t *dest2, const uint8_t *src, size_t n)
+{
+       const uint8_t *limit = src + n;
+       size_t consumed = 0;
+
+       // Align end to 32 bytes.
+       limit = (const uint8_t *)(intptr_t(limit) & ~31);
+
+       if (src >= limit) {
+               return 0;
+       }
+
+       // Process [0,31] bytes, such that start gets aligned to 32 bytes.
+       const uint8_t *aligned_src = (const uint8_t *)(intptr_t(src + 31) & ~31);
+       if (aligned_src != src) {
+               size_t n2 = aligned_src - src;
+               memcpy_interleaved_slow(dest1, dest2, src, n2);
+               dest1 += n2 / 2;
+               dest2 += n2 / 2;
+               if (n2 % 2) {
+                       swap(dest1, dest2);
+               }
+               src = aligned_src;
+               consumed += n2;
+       }
+
+       // Make the length a multiple of 64.
+       if (((limit - src) % 64) != 0) {
+               limit -= 32;
+       }
+       assert(((limit - src) % 64) == 0);
+
+#if __AVX2__
+       const __m256i * __restrict in = (const __m256i *)src;
+       __m256i * __restrict out1 = (__m256i *)dest1;
+       __m256i * __restrict out2 = (__m256i *)dest2;
+
+       __m256i shuffle_cw = _mm256_set_epi8(
+               15, 13, 11, 9, 7, 5, 3, 1, 14, 12, 10, 8, 6, 4, 2, 0,
+               15, 13, 11, 9, 7, 5, 3, 1, 14, 12, 10, 8, 6, 4, 2, 0);
+       while (in < (const __m256i *)limit) {
+               // Note: For brevity, comments show lanes as if they were 2x64-bit (they're actually 2x128).
+               __m256i data1 = _mm256_stream_load_si256(in);         // AaBbCcDd EeFfGgHh
+               __m256i data2 = _mm256_stream_load_si256(in + 1);     // IiJjKkLl MmNnOoPp
+
+               data1 = _mm256_shuffle_epi8(data1, shuffle_cw);       // ABCDabcd EFGHefgh
+               data2 = _mm256_shuffle_epi8(data2, shuffle_cw);       // IJKLijkl MNOPmnop
+       
+               data1 = _mm256_permute4x64_epi64(data1, 0b11011000);  // ABCDEFGH abcdefgh
+               data2 = _mm256_permute4x64_epi64(data2, 0b11011000);  // IJKLMNOP ijklmnop
+
+               __m256i lo = _mm256_permute2x128_si256(data1, data2, 0b00100000);
+               __m256i hi = _mm256_permute2x128_si256(data1, data2, 0b00110001);
+
+               _mm256_storeu_si256(out1, lo);
+               _mm256_storeu_si256(out2, hi);
+
+               in += 2;
+               ++out1;
+               ++out2;
+               consumed += 64;
+       }
+#else
+       const __m128i * __restrict in = (const __m128i *)src;
+       __m128i * __restrict out1 = (__m128i *)dest1;
+       __m128i * __restrict out2 = (__m128i *)dest2;
+
+       __m128i mask_lower_byte = _mm_set1_epi16(0x00ff);
+       while (in < (const __m128i *)limit) {
+               __m128i data1 = _mm_load_si128(in);
+               __m128i data2 = _mm_load_si128(in + 1);
+               __m128i data1_lo = _mm_and_si128(data1, mask_lower_byte);
+               __m128i data2_lo = _mm_and_si128(data2, mask_lower_byte);
+               __m128i data1_hi = _mm_srli_epi16(data1, 8);
+               __m128i data2_hi = _mm_srli_epi16(data2, 8);
+               __m128i lo = _mm_packus_epi16(data1_lo, data2_lo);
+               _mm_storeu_si128(out1, lo);
+               __m128i hi = _mm_packus_epi16(data1_hi, data2_hi);
+               _mm_storeu_si128(out2, hi);
+
+               in += 2;
+               ++out1;
+               ++out2;
+               consumed += 32;
+       }
+#endif
+
+       return consumed;
+}
+
+#endif  // defined(__SSE2__)
+
+void memcpy_interleaved(uint8_t *dest1, uint8_t *dest2, const uint8_t *src, size_t n)
+{
+#ifdef __SSE2__
+       size_t consumed = memcpy_interleaved_fastpath(dest1, dest2, src, n);
+       src += consumed;
+       dest1 += consumed / 2;
+       dest2 += consumed / 2;
+       if (consumed % 2) {
+               swap(dest1, dest2);
+       }
+       n -= consumed;
+
+       if (n > 0) {
+               memcpy_interleaved_slow(dest1, dest2, src, n);
+       }
+#else
+       memcpy_interleaved_slow(dest1, dest2, src, n);
+#endif
+}