[lonetix/smallbytecopy] Add optimized routines for small byte buffer copies.

2021-10-18 11:57:17 +02:00 · 2021-10-18 11:57:17 +02:00 · d7c7060cb7
parent bfdde40031
commit d7c7060cb7
1 changed files with 143 additions and 0 deletions
--- a/lonetix/smallbytecopy.h
+++ b/lonetix/smallbytecopy.h
@ -0,0 +1,143 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+
+/**
+ * \file smallbytecopy.h
+ *
+ * Optimized routines for tiny buffer copy (<= 64 bytes).
+ *
+ * Whenever possible, avoid these routines and use regular
+ * memcpy()/memmove().
+ * These routines are recommended only when:
+ * - you are absolutely sure of the maximum size of your data.
+ * - the compiler cannot possibly estimate it statically,
+ *   otherwise the compiler could do a much better job at
+ *   optimizing the copy.
+ *
+ * \copyright The DoubleFourteen Code Forge (C) All Rights Reserved
+ * \author    Lorenzo Cogotti
+ */
+
+#ifndef DF_SMALLBYTECOPY_H_
+#define DF_SMALLBYTECOPY_H_
+
+#include "xpt.h"
+
+#if defined(__i386__) || defined(__x86_64__)
+#include <assert.h>
+
+// Optimize copy and don't pay attention to alignment,
+// ugly but fast and inline-able compared to plain memcpy()...
+
+#define _bytecopy1(d, s)  ((void) (*(Uint8 *)  (d) = *(Uint8 *)  (s)))
+#define _bytecopy2(d, s)  ((void) (*(Uint16 *) (d) = *(Uint16 *) (s)))
+#define _bytecopy4(d, s)  ((void) (*(Uint32 *) (d) = *(Uint32 *) (s)))
+#define _bytecopy8(d, s)  ((void) (*(Uint64 *) (d) = *(Uint64 *) (s)))
+
+INLINE void _smallbytecopy4(void *__restrict dest, const void *__restrict src, size_t n)
+{
+	Uint8 *d = (Uint8 *) dest, *s = (Uint8 *) src;
+
+	assert(n <= 4);
+
+	switch (n) {
+	case 4:  _bytecopy4(d, s);
+	         break;
+	case 3:  _bytecopy2(d + 1, s + 1);
+	         /*FALLTHROUGH*/
+	case 1:  _bytecopy1(d, s);
+	         break;
+	case 2:  _bytecopy2(d, s);
+	         break;
+	case 0:  break;
+	default: UNREACHABLE; break;
+	}
+}
+
+INLINE void _smallbytecopy8(void *__restrict dest, const void *__restrict src, size_t n)
+{
+	Uint8 *d = (Uint8 *) dest, *s = (Uint8 *) src;
+
+	assert(n <= 8);
+
+	switch (n) {
+	case 8:  _bytecopy8(d, s);
+	         break;
+	case 7:  _bytecopy4(d + 3, s + 3);
+	         /*FALLTHROUGH*/
+	case 3:  _bytecopy2(d + 1, s + 1);
+	         /*FALLTHROUGH*/
+	case 1:  _bytecopy1(d, s);
+	         break;
+	case 6:  _bytecopy4(d + 2, s + 2);
+	         /*FALLTHROUGH*/
+	case 2:  _bytecopy2(d, s);
+	         break;
+	case 5:  _bytecopy1(d + 4, s + 4);
+	         /*FALLTHROUGH*/
+	case 4:  _bytecopy4(d, s);
+	         break;
+	case 0:  break;
+	default: UNREACHABLE; break;
+	}
+}
+
+INLINE void _smallbytecopy16(void *__restrict dest, const void *__restrict src, size_t n)
+{
+	Uint8 *d = (Uint8 *) dest, *s = (Uint8 *) src;
+
+	assert(n <= 16);
+
+	if (n > 8) {
+		_bytecopy8(d, s);
+		d += 8, s += 8, n -= 8;
+	}
+	_smallbytecopy8(d, s, n);
+}
+
+INLINE void _smallbytecopy32(void *__restrict dest, const void *__restrict src, size_t n)
+{
+	Uint8 *d = (Uint8 *) dest, *s = (Uint8 *) src;
+
+	assert(n <= 32);
+
+	if (n > 16) {
+		_bytecopy8(d, s);
+		_bytecopy8(d + 8, s + 8);
+		d += 16, s += 16, n -= 16;
+	}
+	_smallbytecopy16(d, s, n);
+}
+
+INLINE void _smallbytecopy64(void *__restrict dest, const void *__restrict src, size_t n)
+{
+	Uint8 *d = (Uint8 *) dest, *s = (Uint8 *) src;
+
+	assert(n <= 64);
+
+	if (n > 32) {
+		_bytecopy8(d, s);
+		_bytecopy8(d + 8,  s + 8);
+		_bytecopy8(d + 16, s + 16);
+		_bytecopy8(d + 24, s + 24);
+		d += 32, s += 32, n -= 32;
+	}
+	_smallbytecopy32(d, s, n);
+}
+
+#undef _bytecopy1
+#undef _bytecopy2
+#undef _bytecopy4
+#undef _bytecopy8
+
+#else
+#include <string.h>
+
+#define _smallbytecopy4(d, s, n)  ((void) memcpy(d, s, n))
+#define _smallbytecopy8(d, s, n)  ((void) memcpy(d, s, n))
+#define _smallbytecopy16(d, s, n) ((void) memcpy(d, s, n))
+#define _smallbytecopy32(d, s, n) ((void) memcpy(d, s, n))
+#define _smallbytecopy64(d, s, n) ((void) memcpy(d, s, n))
+
+#endif
+
+#endif