linux/arch/alpha/include/asm/word-at-a-time.h
Michael Cree f2db633d30 alpha: Use new generic strncpy_from_user() and strnlen_user()
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>
2012-08-19 08:41:18 -07:00

56 lines
1.2 KiB
C

#ifndef _ASM_WORD_AT_A_TIME_H
#define _ASM_WORD_AT_A_TIME_H
#include <asm/compiler.h>
/*
* word-at-a-time interface for Alpha.
*/
/*
* We do not use the word_at_a_time struct on Alpha, but it needs to be
* implemented to humour the generic code.
*/
struct word_at_a_time {
const unsigned long unused;
};
#define WORD_AT_A_TIME_CONSTANTS { 0 }
/* Return nonzero if val has a zero */
static inline unsigned long has_zero(unsigned long val, unsigned long *bits, const struct word_at_a_time *c)
{
unsigned long zero_locations = __kernel_cmpbge(0, val);
*bits = zero_locations;
return zero_locations;
}
static inline unsigned long prep_zero_mask(unsigned long val, unsigned long bits, const struct word_at_a_time *c)
{
return bits;
}
#define create_zero_mask(bits) (bits)
static inline unsigned long find_zero(unsigned long bits)
{
#if defined(CONFIG_ALPHA_EV6) && defined(CONFIG_ALPHA_EV67)
/* Simple if have CIX instructions */
return __kernel_cttz(bits);
#else
unsigned long t1, t2, t3;
/* Retain lowest set bit only */
bits &= -bits;
/* Binary search for lowest set bit */
t1 = bits & 0xf0;
t2 = bits & 0xcc;
t3 = bits & 0xaa;
if (t1) t1 = 4;
if (t2) t2 = 2;
if (t3) t3 = 1;
return t1 + t2 + t3;
#endif
}
#endif /* _ASM_WORD_AT_A_TIME_H */