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Similar to x86/sparc/powerpc implementations except: 1) we implement an extremely efficient has_zero()/find_zero() sequence with both prep_zero_mask() and create_zero_mask() no-operations. 2) Our output from prep_zero_mask() differs in that only the lowest eight bits are used to represent the zero bytes nevertheless it can be safely ORed with other similar masks from prep_zero_mask() and forms input to create_zero_mask(), the two fundamental properties prep_zero_mask() must satisfy. Tests on EV67 and EV68 CPUs revealed that the generic code is essentially as fast (to within 0.5% of CPU cycles) of the old Alpha specific code for large quadword-aligned strings, despite the 30% extra CPU instructions executed. In contrast, the generic code for unaligned strings is substantially slower (by more than a factor of 3) than the old Alpha specific code. Signed-off-by: Michael Cree <mcree@orcon.net.nz> Acked-by: Matt Turner <mattst88@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
55 lines
1.2 KiB
C
55 lines
1.2 KiB
C
#ifndef _ASM_WORD_AT_A_TIME_H
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#define _ASM_WORD_AT_A_TIME_H
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#include <asm/compiler.h>
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/*
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* word-at-a-time interface for Alpha.
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*/
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/*
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* We do not use the word_at_a_time struct on Alpha, but it needs to be
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* implemented to humour the generic code.
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*/
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struct word_at_a_time {
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const unsigned long unused;
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};
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#define WORD_AT_A_TIME_CONSTANTS { 0 }
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/* Return nonzero if val has a zero */
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static inline unsigned long has_zero(unsigned long val, unsigned long *bits, const struct word_at_a_time *c)
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{
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unsigned long zero_locations = __kernel_cmpbge(0, val);
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*bits = zero_locations;
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return zero_locations;
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}
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static inline unsigned long prep_zero_mask(unsigned long val, unsigned long bits, const struct word_at_a_time *c)
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{
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return bits;
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}
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#define create_zero_mask(bits) (bits)
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static inline unsigned long find_zero(unsigned long bits)
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{
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#if defined(CONFIG_ALPHA_EV6) && defined(CONFIG_ALPHA_EV67)
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/* Simple if have CIX instructions */
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return __kernel_cttz(bits);
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#else
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unsigned long t1, t2, t3;
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/* Retain lowest set bit only */
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bits &= -bits;
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/* Binary search for lowest set bit */
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t1 = bits & 0xf0;
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t2 = bits & 0xcc;
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t3 = bits & 0xaa;
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if (t1) t1 = 4;
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if (t2) t2 = 2;
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if (t3) t3 = 1;
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return t1 + t2 + t3;
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#endif
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}
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#endif /* _ASM_WORD_AT_A_TIME_H */
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