Optimise memchr for NEON-enabled processors
This commit is contained in:
Prakhar Bahuguna
committed by
Corinna Vinschen
Corinna Vinschen
parent
c6c7dfc493
commit
c47c9bdc1b
@@ -29,7 +29,9 @@
|
||||
|
||||
#include "acle-compat.h"
|
||||
|
||||
#if __ARM_ARCH_ISA_THUMB >= 2 && defined (__ARM_FEATURE_DSP)
|
||||
#if defined (__ARM_NEON__) || defined (__ARM_NEON)
|
||||
/* Defined in memchr.S. */
|
||||
#elif __ARM_ARCH_ISA_THUMB >= 2 && defined (__ARM_FEATURE_DSP)
|
||||
/* Defined in memchr.S. */
|
||||
#else
|
||||
# include "../../string/memchr.c"
|
||||
|
||||
@@ -78,7 +78,188 @@
|
||||
#include "acle-compat.h"
|
||||
|
||||
@ NOTE: This ifdef MUST match the one in memchr-stub.c
|
||||
#if __ARM_ARCH_ISA_THUMB >= 2 && defined (__ARM_FEATURE_DSP)
|
||||
#if defined (__ARM_NEON__) || defined (__ARM_NEON)
|
||||
.arch armv7-a
|
||||
.fpu neon
|
||||
|
||||
|
||||
/* Arguments */
|
||||
#define srcin r0
|
||||
#define chrin r1
|
||||
#define cntin r2
|
||||
|
||||
/* Retval */
|
||||
#define result r0 /* Live range does not overlap with srcin */
|
||||
|
||||
/* Working registers */
|
||||
#define src r1 /* Live range does not overlap with chrin */
|
||||
#define tmp r3
|
||||
#define synd r0 /* No overlap with srcin or result */
|
||||
#define soff r12
|
||||
|
||||
/* Working NEON registers */
|
||||
#define vrepchr q0
|
||||
#define vdata0 q1
|
||||
#define vdata0_0 d2 /* Lower half of vdata0 */
|
||||
#define vdata0_1 d3 /* Upper half of vdata0 */
|
||||
#define vdata1 q2
|
||||
#define vdata1_0 d4 /* Lower half of vhas_chr0 */
|
||||
#define vdata1_1 d5 /* Upper half of vhas_chr0 */
|
||||
#define vrepmask q3
|
||||
#define vrepmask0 d6
|
||||
#define vrepmask1 d7
|
||||
#define vend q4
|
||||
#define vend0 d8
|
||||
#define vend1 d9
|
||||
|
||||
/*
|
||||
* Core algorithm:
|
||||
*
|
||||
* For each 32-byte chunk we calculate a 32-bit syndrome value, with one bit per
|
||||
* byte. Each bit is set if the relevant byte matched the requested character
|
||||
* and cleared otherwise. Since the bits in the syndrome reflect exactly the
|
||||
* order in which things occur in the original string, counting trailing zeros
|
||||
* allows to identify exactly which byte has matched.
|
||||
*/
|
||||
|
||||
.text
|
||||
.thumb_func
|
||||
.align 4
|
||||
.p2align 4,,15
|
||||
.global memchr
|
||||
.type memchr,%function
|
||||
|
||||
memchr:
|
||||
.cfi_sections .debug_frame
|
||||
.cfi_startproc
|
||||
/* Use a simple loop if there are less than 8 bytes to search. */
|
||||
cmp cntin, #7
|
||||
bhi .Llargestr
|
||||
|
||||
.Lsmallstr:
|
||||
subs cntin, cntin, #1
|
||||
blt .Lnotfound /* Return not found if reached end. */
|
||||
ldrb tmp, [srcin], #1
|
||||
cmp tmp, chrin
|
||||
bne .Lsmallstr /* Loop again if not found. */
|
||||
/* Otherwise fixup address and return. */
|
||||
sub result, result, #1
|
||||
bx lr
|
||||
|
||||
|
||||
.Llargestr:
|
||||
vdup.8 vrepchr, chrin /* Duplicate char across all lanes. */
|
||||
/*
|
||||
* Magic constant 0x8040201008040201 allows us to identify which lane
|
||||
* matches the requested byte.
|
||||
*/
|
||||
movw tmp, #0x0201
|
||||
movt tmp, #0x0804
|
||||
lsl soff, tmp, #4
|
||||
vmov vrepmask0, tmp, soff
|
||||
vmov vrepmask1, tmp, soff
|
||||
/* Work with aligned 32-byte chunks */
|
||||
bic src, srcin, #31
|
||||
ands soff, srcin, #31
|
||||
beq .Lloopintro /* Go straight to main loop if it's aligned. */
|
||||
|
||||
/*
|
||||
* Input string is not 32-byte aligned. We calculate the syndrome
|
||||
* value for the aligned 32 bytes block containing the first bytes
|
||||
* and mask the irrelevant part.
|
||||
*/
|
||||
vld1.8 {vdata0, vdata1}, [src:256]!
|
||||
sub tmp, soff, #32
|
||||
adds cntin, cntin, tmp
|
||||
vceq.i8 vdata0, vdata0, vrepchr
|
||||
vceq.i8 vdata1, vdata1, vrepchr
|
||||
vand vdata0, vdata0, vrepmask
|
||||
vand vdata1, vdata1, vrepmask
|
||||
vpadd.i8 vdata0_0, vdata0_0, vdata0_1
|
||||
vpadd.i8 vdata1_0, vdata1_0, vdata1_1
|
||||
vpadd.i8 vdata0_0, vdata0_0, vdata1_0
|
||||
vpadd.i8 vdata0_0, vdata0_0, vdata0_0
|
||||
vmov synd, vdata0_0[0]
|
||||
|
||||
/* Clear the soff lower bits */
|
||||
lsr synd, synd, soff
|
||||
lsl synd, synd, soff
|
||||
/* The first block can also be the last */
|
||||
bls .Lmasklast
|
||||
/* Have we found something already? */
|
||||
cbnz synd, .Ltail
|
||||
|
||||
|
||||
.Lloopintro:
|
||||
vpush {vend}
|
||||
/* 264/265 correspond to d8/d9 for q4 */
|
||||
.cfi_adjust_cfa_offset 16
|
||||
.cfi_rel_offset 264, 0
|
||||
.cfi_rel_offset 265, 8
|
||||
.p2align 3,,7
|
||||
.Lloop:
|
||||
vld1.8 {vdata0, vdata1}, [src:256]!
|
||||
subs cntin, cntin, #32
|
||||
vceq.i8 vdata0, vdata0, vrepchr
|
||||
vceq.i8 vdata1, vdata1, vrepchr
|
||||
/* If we're out of data we finish regardless of the result. */
|
||||
bls .Lend
|
||||
/* Use a fast check for the termination condition. */
|
||||
vorr vend, vdata0, vdata1
|
||||
vorr vend0, vend0, vend1
|
||||
vmov synd, tmp, vend0
|
||||
orrs synd, synd, tmp
|
||||
/* We're not out of data, loop if we haven't found the character. */
|
||||
beq .Lloop
|
||||
|
||||
.Lend:
|
||||
vpop {vend}
|
||||
.cfi_adjust_cfa_offset -16
|
||||
.cfi_restore 264
|
||||
.cfi_restore 265
|
||||
|
||||
/* Termination condition found, let's calculate the syndrome value. */
|
||||
vand vdata0, vdata0, vrepmask
|
||||
vand vdata1, vdata1, vrepmask
|
||||
vpadd.i8 vdata0_0, vdata0_0, vdata0_1
|
||||
vpadd.i8 vdata1_0, vdata1_0, vdata1_1
|
||||
vpadd.i8 vdata0_0, vdata0_0, vdata1_0
|
||||
vpadd.i8 vdata0_0, vdata0_0, vdata0_0
|
||||
vmov synd, vdata0_0[0]
|
||||
cbz synd, .Lnotfound
|
||||
bhi .Ltail
|
||||
|
||||
|
||||
.Lmasklast:
|
||||
/* Clear the (-cntin) upper bits to avoid out-of-bounds matches. */
|
||||
neg cntin, cntin
|
||||
lsl synd, synd, cntin
|
||||
lsrs synd, synd, cntin
|
||||
it eq
|
||||
moveq src, #0 /* If no match, set src to 0 so the retval is 0. */
|
||||
|
||||
|
||||
.Ltail:
|
||||
/* Count the trailing zeros using bit reversing */
|
||||
rbit synd, synd
|
||||
/* Compensate the last post-increment */
|
||||
sub src, src, #32
|
||||
/* Count the leading zeros */
|
||||
clz synd, synd
|
||||
/* Compute the potential result and return */
|
||||
add result, src, synd
|
||||
bx lr
|
||||
|
||||
|
||||
.Lnotfound:
|
||||
/* Set result to NULL if not found and return */
|
||||
mov result, #0
|
||||
bx lr
|
||||
|
||||
.cfi_endproc
|
||||
.size memchr, . - memchr
|
||||
|
||||
#elif __ARM_ARCH_ISA_THUMB >= 2 && defined (__ARM_FEATURE_DSP)
|
||||
|
||||
#if __ARM_ARCH_PROFILE == 'M'
|
||||
.arch armv7e-m
|
||||
|
||||
Reference in New Issue
Block a user