/* SPDX-License-Identifier: GPL-2.0 */ #ifndef _ASM_HASH_H #define _ASM_HASH_H /* * Fortunately, most people who want to run Linux on Microblaze enable * both multiplier and barrel shifter, but omitting them is technically * a supported configuration. * * With just a barrel shifter, we can implement an efficient constant * multiply using shifts and adds. GCC can find a 9-step solution, but * this 6-step solution was found by Yevgen Voronenko's implementation * of the Hcub algorithm at http://spiral.ece.cmu.edu/mcm/gen.html. * * That software is really not designed for a single multiplier this large, * but if you run it enough times with different seeds, it'll find several * 6-shift, 6-add sequences for computing x * 0x61C88647. They are all * c = (x << 19) + x; * a = (x << 9) + c; * b = (x << 23) + a; * return (a<<11) + (b<<6) + (c<<3) - b; * with variations on the order of the final add. * * Without even a shifter, it's hopless; any hash function will suck. */ #if CONFIG_XILINX_MICROBLAZE0_USE_HW_MUL == 0 #define HAVE_ARCH__HASH_32 1 /* Multiply by GOLDEN_RATIO_32 = 0x61C88647 */ static inline u32 __attribute_const__ __hash_32(u32 a) { #if CONFIG_XILINX_MICROBLAZE0_USE_BARREL unsigned int b, c; /* Phase 1: Compute three intermediate values */ b = a << 23; c = (a << 19) + a; a = (a << 9) + c; b += a; /* Phase 2: Compute (a << 11) + (b << 6) + (c << 3) - b */ a <<= 5; a += b; /* (a << 5) + b */ a <<= 3; a += c; /* (a << 8) + (b << 3) + c */ a <<= 3; return a - b; /* (a << 11) + (b << 6) + (c << 3) - b */ #else /* * "This is really going to hurt." * * Without a barrel shifter, left shifts are implemented as * repeated additions, and the best we can do is an optimal * addition-subtraction chain. This one is not known to be * optimal, but at 37 steps, it's decent for a 31-bit multiplier. * * Question: given its size (37*4 = 148 bytes per instance), * and slowness, is this worth having inline? */ unsigned int b, c, d; b = a << 4; /* 4 */ c = b << 1; /* 1 5 */ b += a; /* 1 6 */ c += b; /* 1 7 */ c <<= 3; /* 3 10 */ c -= a; /* 1 11 */ d = c << 7; /* 7 18 */ d += b; /* 1 19 */ d <<= 8; /* 8 27 */ d += a; /* 1 28 */ d <<= 1; /* 1 29 */ d += b; /* 1 30 */ d <<= 6; /* 6 36 */ return d + c; /* 1 37 total instructions*/ #endif } #endif /* !CONFIG_XILINX_MICROBLAZE0_USE_HW_MUL */ #endif /* _ASM_HASH_H */
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Kbuild | File | 742 B | 0644 |
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asm-compat.h | File | 518 B | 0644 |
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asm-offsets.h | File | 35 B | 0644 |
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atomic.h | File | 626 B | 0644 |
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cache.h | File | 644 B | 0644 |
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cacheflush.h | File | 4.12 KB | 0644 |
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checksum.h | File | 942 B | 0644 |
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cmpxchg.h | File | 919 B | 0644 |
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cpuinfo.h | File | 2.13 KB | 0644 |
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cputable.h | File | 1 B | 0644 |
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current.h | File | 850 B | 0644 |
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delay.h | File | 2.26 KB | 0644 |
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dma-mapping.h | File | 765 B | 0644 |
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dma.h | File | 706 B | 0644 |
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elf.h | File | 738 B | 0644 |
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entry.h | File | 1.13 KB | 0644 |
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exceptions.h | File | 2.08 KB | 0644 |
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fixmap.h | File | 1.96 KB | 0644 |
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flat.h | File | 2.26 KB | 0644 |
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ftrace.h | File | 641 B | 0644 |
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futex.h | File | 2.13 KB | 0644 |
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hash.h | File | 2.37 KB | 0644 |
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highmem.h | File | 2.2 KB | 0644 |
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hw_irq.h | File | 1 B | 0644 |
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io.h | File | 2.05 KB | 0644 |
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irq.h | File | 538 B | 0644 |
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irqflags.h | File | 2.6 KB | 0644 |
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kgdb.h | File | 739 B | 0644 |
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mmu.h | File | 4.19 KB | 0644 |
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mmu_context.h | File | 141 B | 0644 |
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mmu_context_mm.h | File | 3.91 KB | 0644 |
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module.h | File | 840 B | 0644 |
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page.h | File | 6.11 KB | 0644 |
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pci-bridge.h | File | 4.57 KB | 0644 |
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pci.h | File | 2.47 KB | 0644 |
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pgalloc.h | File | 4.74 KB | 0644 |
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pgtable.h | File | 17.66 KB | 0644 |
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processor.h | File | 4.11 KB | 0644 |
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prom.h | File | 713 B | 0644 |
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ptrace.h | File | 727 B | 0644 |
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pvr.h | File | 8.72 KB | 0644 |
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registers.h | File | 1.65 KB | 0644 |
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seccomp.h | File | 256 B | 0644 |
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sections.h | File | 637 B | 0644 |
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setup.h | File | 1.37 KB | 0644 |
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string.h | File | 630 B | 0644 |
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switch_to.h | File | 629 B | 0644 |
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syscall.h | File | 2.26 KB | 0644 |
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thread_info.h | File | 4.01 KB | 0644 |
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timex.h | File | 402 B | 0644 |
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tlb.h | File | 714 B | 0644 |
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tlbflush.h | File | 2.04 KB | 0644 |
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uaccess.h | File | 9.98 KB | 0644 |
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unaligned.h | File | 871 B | 0644 |
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unistd.h | File | 1.19 KB | 0644 |
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unwind.h | File | 719 B | 0644 |
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user.h | File | 1 B | 0644 |
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