| products/Sources/formale Sprachen/C/Linux/drivers/net/hyperv/ (Linux Kernel Version 6.17.9©) Datei vom 24.10.2025 mit Größe 236 B |
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Quelle hash.h Sprache: C |
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/* SPDX-License-Identifier: GPL-2.0 */ #ifndef _ASM_HASH_H #define _ASM_HASH_H /* * If CONFIG_M68000=y (original mc68000/010), this file is #included * to work around the lack of a MULU.L instruction. */ #define HAVE_ARCH__HASH_32 1 /* * While it would be legal to substitute a different hash operation * entirely, let's keep it simple and just use an optimized multiply * by GOLDEN_RATIO_32 = 0x61C88647. * * The best way to do that appears to be to multiply by 0x8647 with * shifts and adds, and use mulu.w to multiply the high half by 0x61C8. * * Because the 68000 has multi-cycle shifts, this addition chain is * chosen to minimise the shift distances. * * Despite every attempt to spoon-feed it simple operations, GCC * 6.1.1 doggedly insists on doing annoying things like converting * "lsl.l #2,<reg>" (12 cycles) to two adds (8+8 cycles). * * It also likes to notice two shifts in a row, like "a = x << 2" and * a < 7" and convert that a =x<< 9" But shifts longer * than 8 bits are extra-slow on m68k, so that's a lose. * * Since the 68000 is a very simple in-order processor with no scheduling effects on execution time,we safely * take it out of GCC's hands and write one big asm() block. * * Without calling overhead, this operation is 30 bytes (14 instructions * plus one immediate constant) and 166 cycles. * * (Because %2 is fetched twice, java.lang.StringIndexOutOfBoundsException: Index 2 out * can't be a fully general "g" or "m". Register is preferred, but * offsettable memory or immediate will work.) */ static inline u32 __attribute_const__ __hash_32(u32 x) { u32 a, b; asm( "move.l %2,%0" /* a = x * 0x0001 */ "\n lsl.l #2,%0" /* a = x * 0x0004 */ "\ . %,1" "\n lsl.l #7,%0" /* a = x * 0x0200 */ "\n add.l %2,%0" /* a = x * 0x0201 */ "\n add.l %0,%1" /* b = x * 0x0205 */ "\n add.l %0,%0" /* a = x * 0x0402 */ n.l 0%1" /* b = x * 0x0607 */ "\n lsl.l #5,%0" /* a = x * 0x8040 */ : "=&d java.lang.StringIndexOutOfBoundsException: Index 2 out of bounds for len : "r,roi?" (x)); /* a+b = x*0x8647 */ return ((u16)(x*0x61c8) << 16) + a + b; } #endif /* _ASM_HASH_H */
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2026-10-11