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This patch implements the word-at-a-time interface for ARM using the same algorithm as x86. We use the fls macro from ARMv5 onwards, where we have a clz instruction available which saves us a mov instruction when targetting Thumb-2. For older CPUs, we use the magic 0x0ff0001 constant. Big-endian configurations make use of the implementation from asm-generic. With this implemented, we can replace our byte-at-a-time strnlen_user and strncpy_from_user functions with the optimised generic versions. Reviewed-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
56 lines
1.1 KiB
C
56 lines
1.1 KiB
C
#ifndef __ASM_ARM_WORD_AT_A_TIME_H
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#define __ASM_ARM_WORD_AT_A_TIME_H
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#ifndef __ARMEB__
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/*
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* Little-endian word-at-a-time zero byte handling.
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* Heavily based on the x86 algorithm.
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*/
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#include <linux/kernel.h>
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struct word_at_a_time {
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const unsigned long one_bits, high_bits;
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};
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#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0x01), REPEAT_BYTE(0x80) }
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static inline unsigned long has_zero(unsigned long a, unsigned long *bits,
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const struct word_at_a_time *c)
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{
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unsigned long mask = ((a - c->one_bits) & ~a) & c->high_bits;
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*bits = mask;
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return mask;
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}
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#define prep_zero_mask(a, bits, c) (bits)
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static inline unsigned long create_zero_mask(unsigned long bits)
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{
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bits = (bits - 1) & ~bits;
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return bits >> 7;
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}
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static inline unsigned long find_zero(unsigned long mask)
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{
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unsigned long ret;
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#if __LINUX_ARM_ARCH__ >= 5
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/* We have clz available. */
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ret = fls(mask) >> 3;
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#else
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/* (000000 0000ff 00ffff ffffff) -> ( 1 1 2 3 ) */
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ret = (0x0ff0001 + mask) >> 23;
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/* Fix the 1 for 00 case */
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ret &= mask;
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#endif
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return ret;
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}
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#else /* __ARMEB__ */
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#include <asm-generic/word-at-a-time.h>
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#endif
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#endif /* __ASM_ARM_WORD_AT_A_TIME_H */
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