# commit db9b4570c5dc550074140ac1d1677077fba29a26
# Author: Alan Modra <amodra@gmail.com>
# Date: Sat Aug 17 18:40:11 2013 +0930
#
# PowerPC LE strlen
# http://sourceware.org/ml/libc-alpha/2013-08/msg00097.html
#
# This is the first of nine patches adding little-endian support to the
# existing optimised string and memory functions. I did spend some
# time with a power7 simulator looking at cycle by cycle behaviour for
# memchr, but most of these patches have not been run on cpu simulators
# to check that we are going as fast as possible. I'm sure PowerPC can
# do better. However, the little-endian support mostly leaves main
# loops unchanged, so I'm banking on previous authors having done a
# good job on big-endian.. As with most code you stare at long enough,
# I found some improvements for big-endian too.
#
# Little-endian support for strlen. Like most of the string functions,
# I leave the main word or multiple-word loops substantially unchanged,
# just needing to modify the tail.
#
# Removing the branch in the power7 functions is just a tidy. .align
# produces a branch anyway. Modifying regs in the non-power7 functions
# is to suit the new little-endian tail.
#
# * sysdeps/powerpc/powerpc64/power7/strlen.S (strlen): Add little-endian
# support. Don't branch over align.
# * sysdeps/powerpc/powerpc32/power7/strlen.S: Likewise.
# * sysdeps/powerpc/powerpc64/strlen.S (strlen): Add little-endian support.
# Rearrange tmp reg use to suit. Comment.
# * sysdeps/powerpc/powerpc32/strlen.S: Likewise.
#
diff -urN glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/power7/strlen.S glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/power7/strlen.S
--- glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/power7/strlen.S 2014-05-28 12:28:44.000000000 -0500
+++ glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/power7/strlen.S 2014-05-28 12:28:45.000000000 -0500
@@ -31,7 +31,11 @@
li r0,0 /* Word with null chars to use with cmpb. */
li r5,-1 /* MASK = 0xffffffffffffffff. */
lwz r12,0(r4) /* Load word from memory. */
+#ifdef __LITTLE_ENDIAN__
+ slw r5,r5,r6
+#else
srw r5,r5,r6 /* MASK = MASK >> padding. */
+#endif
orc r9,r12,r5 /* Mask bits that are not part of the string. */
cmpb r10,r9,r0 /* Check for null bytes in WORD1. */
cmpwi cr7,r10,0 /* If r10 == 0, no null's have been found. */
@@ -49,9 +53,6 @@
cmpb r10,r12,r0
cmpwi cr7,r10,0
bne cr7,L(done)
- b L(loop) /* We branch here (rather than falling through)
- to skip the nops due to heavy alignment
- of the loop below. */
/* Main loop to look for the end of the string. Since it's a
small loop (< 8 instructions), align it to 32-bytes. */
@@ -88,9 +89,15 @@
0xff in the same position as the null byte in the original
word from the string. Use that to calculate the length. */
L(done):
- cntlzw r0,r10 /* Count leading zeroes before the match. */
+#ifdef __LITTLE_ENDIAN__
+ addi r9, r10, -1 /* Form a mask from trailing zeros. */
+ andc r9, r9, r10
+ popcntw r0, r9 /* Count the bits in the mask. */
+#else
+ cntlzw r0,r10 /* Count leading zeros before the match. */
+#endif
subf r5,r3,r4
- srwi r0,r0,3 /* Convert leading zeroes to bytes. */
+ srwi r0,r0,3 /* Convert leading zeros to bytes. */
add r3,r5,r0 /* Compute final length. */
blr
END (BP_SYM (strlen))
diff -urN glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/strlen.S glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/strlen.S
--- glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/strlen.S 2014-05-28 12:28:44.000000000 -0500
+++ glibc-2.17-c758a686/sysdeps/powerpc/powerpc32/strlen.S 2014-05-28 12:32:24.000000000 -0500
@@ -31,7 +31,12 @@
1 is subtracted you get a value in the range 0x00-0x7f, none of which
have their high bit set. The expression here is
(x + 0xfefefeff) & ~(x | 0x7f7f7f7f), which gives 0x00000000 when
- there were no 0x00 bytes in the word.
+ there were no 0x00 bytes in the word. You get 0x80 in bytes that
+ match, but possibly false 0x80 matches in the next more significant
+ byte to a true match due to carries. For little-endian this is
+ of no consequence since the least significant match is the one
+ we're interested in, but big-endian needs method 2 to find which
+ byte matches.
2) Given a word 'x', we can test to see _which_ byte was zero by
calculating ~(((x & 0x7f7f7f7f) + 0x7f7f7f7f) | x | 0x7f7f7f7f).
@@ -74,7 +79,7 @@
ENTRY (BP_SYM (strlen))
-#define rTMP1 r0
+#define rTMP4 r0
#define rRTN r3 /* incoming STR arg, outgoing result */
#define rSTR r4 /* current string position */
#define rPADN r5 /* number of padding bits we prepend to the
@@ -84,9 +89,9 @@
#define rWORD1 r8 /* current string word */
#define rWORD2 r9 /* next string word */
#define rMASK r9 /* mask for first string word */
-#define rTMP2 r10
-#define rTMP3 r11
-#define rTMP4 r12
+#define rTMP1 r10
+#define rTMP2 r11
+#define rTMP3 r12
CHECK_BOUNDS_LOW (rRTN, rTMP1, rTMP2)
@@ -96,15 +101,20 @@
lwz rWORD1, 0(rSTR)
li rMASK, -1
addi r7F7F, r7F7F, 0x7f7f
-/* That's the setup done, now do the first pair of words.
- We make an exception and use method (2) on the first two words, to reduce
- overhead. */
+/* We use method (2) on the first two words, because rFEFE isn't
+ required which reduces setup overhead. Also gives a faster return
+ for small strings on big-endian due to needing to recalculate with
+ method (2) anyway. */
+#ifdef __LITTLE_ENDIAN__
+ slw rMASK, rMASK, rPADN
+#else
srw rMASK, rMASK, rPADN
+#endif
and rTMP1, r7F7F, rWORD1
or rTMP2, r7F7F, rWORD1
add rTMP1, rTMP1, r7F7F
- nor rTMP1, rTMP2, rTMP1
- and. rWORD1, rTMP1, rMASK
+ nor rTMP3, rTMP2, rTMP1
+ and. rTMP3, rTMP3, rMASK
mtcrf 0x01, rRTN
bne L(done0)
lis rFEFE, -0x101
@@ -113,11 +123,12 @@
bt 29, L(loop)
/* Handle second word of pair. */
+/* Perhaps use method (1) here for little-endian, saving one instruction? */
lwzu rWORD1, 4(rSTR)
and rTMP1, r7F7F, rWORD1
or rTMP2, r7F7F, rWORD1
add rTMP1, rTMP1, r7F7F
- nor. rWORD1, rTMP2, rTMP1
+ nor. rTMP3, rTMP2, rTMP1
bne L(done0)
/* The loop. */
@@ -131,29 +142,53 @@
add rTMP3, rFEFE, rWORD2
nor rTMP4, r7F7F, rWORD2
bne L(done1)
- and. rTMP1, rTMP3, rTMP4
+ and. rTMP3, rTMP3, rTMP4
beq L(loop)
+#ifndef __LITTLE_ENDIAN__
and rTMP1, r7F7F, rWORD2
add rTMP1, rTMP1, r7F7F
- andc rWORD1, rTMP4, rTMP1
+ andc rTMP3, rTMP4, rTMP1
b L(done0)
L(done1):
and rTMP1, r7F7F, rWORD1
subi rSTR, rSTR, 4
add rTMP1, rTMP1, r7F7F
- andc rWORD1, rTMP2, rTMP1
+ andc rTMP3, rTMP2, rTMP1
/* When we get to here, rSTR points to the first word in the string that
- contains a zero byte, and the most significant set bit in rWORD1 is in that
- byte. */
+ contains a zero byte, and rTMP3 has 0x80 for bytes that are zero,
+ and 0x00 otherwise. */
L(done0):
- cntlzw rTMP3, rWORD1
+ cntlzw rTMP3, rTMP3
subf rTMP1, rRTN, rSTR
srwi rTMP3, rTMP3, 3
add rRTN, rTMP1, rTMP3
/* GKM FIXME: check high bound. */
blr
+#else
+
+L(done0):
+ addi rTMP1, rTMP3, -1 /* Form a mask from trailing zeros. */
+ andc rTMP1, rTMP1, rTMP3
+ cntlzw rTMP1, rTMP1 /* Count bits not in the mask. */
+ subf rTMP3, rRTN, rSTR
+ subfic rTMP1, rTMP1, 32-7
+ srwi rTMP1, rTMP1, 3
+ add rRTN, rTMP1, rTMP3
+ blr
+
+L(done1):
+ addi rTMP3, rTMP1, -1
+ andc rTMP3, rTMP3, rTMP1
+ cntlzw rTMP3, rTMP3
+ subf rTMP1, rRTN, rSTR
+ subfic rTMP3, rTMP3, 32-7-32
+ srawi rTMP3, rTMP3, 3
+ add rRTN, rTMP1, rTMP3
+ blr
+#endif
+
END (BP_SYM (strlen))
libc_hidden_builtin_def (strlen)
diff -urN glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/power7/strlen.S glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/power7/strlen.S
--- glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/power7/strlen.S 2014-05-28 12:28:44.000000000 -0500
+++ glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/power7/strlen.S 2014-05-28 12:28:45.000000000 -0500
@@ -32,7 +32,11 @@
with cmpb. */
li r5,-1 /* MASK = 0xffffffffffffffff. */
ld r12,0(r4) /* Load doubleword from memory. */
+#ifdef __LITTLE_ENDIAN__
+ sld r5,r5,r6
+#else
srd r5,r5,r6 /* MASK = MASK >> padding. */
+#endif
orc r9,r12,r5 /* Mask bits that are not part of the string. */
cmpb r10,r9,r0 /* Check for null bytes in DWORD1. */
cmpdi cr7,r10,0 /* If r10 == 0, no null's have been found. */
@@ -50,9 +54,6 @@
cmpb r10,r12,r0
cmpdi cr7,r10,0
bne cr7,L(done)
- b L(loop) /* We branch here (rather than falling through)
- to skip the nops due to heavy alignment
- of the loop below. */
/* Main loop to look for the end of the string. Since it's a
small loop (< 8 instructions), align it to 32-bytes. */
@@ -89,9 +90,15 @@
0xff in the same position as the null byte in the original
doubleword from the string. Use that to calculate the length. */
L(done):
- cntlzd r0,r10 /* Count leading zeroes before the match. */
+#ifdef __LITTLE_ENDIAN__
+ addi r9, r10, -1 /* Form a mask from trailing zeros. */
+ andc r9, r9, r10
+ popcntd r0, r9 /* Count the bits in the mask. */
+#else
+ cntlzd r0,r10 /* Count leading zeros before the match. */
+#endif
subf r5,r3,r4
- srdi r0,r0,3 /* Convert leading zeroes to bytes. */
+ srdi r0,r0,3 /* Convert leading/trailing zeros to bytes. */
add r3,r5,r0 /* Compute final length. */
blr
END (BP_SYM (strlen))
diff -urN glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/strlen.S glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/strlen.S
--- glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/strlen.S 2014-05-28 12:28:44.000000000 -0500
+++ glibc-2.17-c758a686/sysdeps/powerpc/powerpc64/strlen.S 2014-05-28 12:38:17.000000000 -0500
@@ -31,7 +31,12 @@
1 is subtracted you get a value in the range 0x00-0x7f, none of which
have their high bit set. The expression here is
(x + 0xfefefeff) & ~(x | 0x7f7f7f7f), which gives 0x00000000 when
- there were no 0x00 bytes in the word.
+ there were no 0x00 bytes in the word. You get 0x80 in bytes that
+ match, but possibly false 0x80 matches in the next more significant
+ byte to a true match due to carries. For little-endian this is
+ of no consequence since the least significant match is the one
+ we're interested in, but big-endian needs method 2 to find which
+ byte matches.
2) Given a word 'x', we can test to see _which_ byte was zero by
calculating ~(((x & 0x7f7f7f7f) + 0x7f7f7f7f) | x | 0x7f7f7f7f).
@@ -64,7 +69,7 @@
Answer:
1) Added a Data Cache Block Touch early to prefetch the first 128
byte cache line. Adding dcbt instructions to the loop would not be
- effective since most strings will be shorter than the cache line.*/
+ effective since most strings will be shorter than the cache line. */
/* Some notes on register usage: Under the SVR4 ABI, we can use registers
0 and 3 through 12 (so long as we don't call any procedures) without
@@ -80,7 +85,7 @@
ENTRY (BP_SYM (strlen))
CALL_MCOUNT 1
-#define rTMP1 r0
+#define rTMP4 r0
#define rRTN r3 /* incoming STR arg, outgoing result */
#define rSTR r4 /* current string position */
#define rPADN r5 /* number of padding bits we prepend to the
@@ -90,9 +95,9 @@
#define rWORD1 r8 /* current string doubleword */
#define rWORD2 r9 /* next string doubleword */
#define rMASK r9 /* mask for first string doubleword */
-#define rTMP2 r10
-#define rTMP3 r11
-#define rTMP4 r12
+#define rTMP1 r10
+#define rTMP2 r11
+#define rTMP3 r12
/* Note: The Bounded pointer support in this code is broken. This code
was inherited from PPC32 and that support was never completed.
@@ -109,30 +114,36 @@
addi r7F7F, r7F7F, 0x7f7f
li rMASK, -1
insrdi r7F7F, r7F7F, 32, 0
-/* That's the setup done, now do the first pair of doublewords.
- We make an exception and use method (2) on the first two doublewords,
- to reduce overhead. */
- srd rMASK, rMASK, rPADN
+/* We use method (2) on the first two doublewords, because rFEFE isn't
+ required which reduces setup overhead. Also gives a faster return
+ for small strings on big-endian due to needing to recalculate with
+ method (2) anyway. */
+#ifdef __LITTLE_ENDIAN__
+ sld rMASK, rMASK, rPADN
+#else
+ srd rMASK, rMASK, rPADN
+#endif
and rTMP1, r7F7F, rWORD1
or rTMP2, r7F7F, rWORD1
lis rFEFE, -0x101
add rTMP1, rTMP1, r7F7F
addi rFEFE, rFEFE, -0x101
- nor rTMP1, rTMP2, rTMP1
- and. rWORD1, rTMP1, rMASK
+ nor rTMP3, rTMP2, rTMP1
+ and. rTMP3, rTMP3, rMASK
mtcrf 0x01, rRTN
bne L(done0)
- sldi rTMP1, rFEFE, 32
- add rFEFE, rFEFE, rTMP1
+ sldi rTMP1, rFEFE, 32
+ add rFEFE, rFEFE, rTMP1
/* Are we now aligned to a doubleword boundary? */
bt 28, L(loop)
/* Handle second doubleword of pair. */
+/* Perhaps use method (1) here for little-endian, saving one instruction? */
ldu rWORD1, 8(rSTR)
and rTMP1, r7F7F, rWORD1
or rTMP2, r7F7F, rWORD1
add rTMP1, rTMP1, r7F7F
- nor. rWORD1, rTMP2, rTMP1
+ nor. rTMP3, rTMP2, rTMP1
bne L(done0)
/* The loop. */
@@ -146,29 +157,53 @@
add rTMP3, rFEFE, rWORD2
nor rTMP4, r7F7F, rWORD2
bne L(done1)
- and. rTMP1, rTMP3, rTMP4
+ and. rTMP3, rTMP3, rTMP4
beq L(loop)
+#ifndef __LITTLE_ENDIAN__
and rTMP1, r7F7F, rWORD2
add rTMP1, rTMP1, r7F7F
- andc rWORD1, rTMP4, rTMP1
+ andc rTMP3, rTMP4, rTMP1
b L(done0)
L(done1):
and rTMP1, r7F7F, rWORD1
subi rSTR, rSTR, 8
add rTMP1, rTMP1, r7F7F
- andc rWORD1, rTMP2, rTMP1
+ andc rTMP3, rTMP2, rTMP1
/* When we get to here, rSTR points to the first doubleword in the string that
- contains a zero byte, and the most significant set bit in rWORD1 is in that
- byte. */
+ contains a zero byte, and rTMP3 has 0x80 for bytes that are zero, and 0x00
+ otherwise. */
L(done0):
- cntlzd rTMP3, rWORD1
+ cntlzd rTMP3, rTMP3
subf rTMP1, rRTN, rSTR
srdi rTMP3, rTMP3, 3
add rRTN, rTMP1, rTMP3
/* GKM FIXME: check high bound. */
blr
+#else
+
+L(done0):
+ addi rTMP1, rTMP3, -1 /* Form a mask from trailing zeros. */
+ andc rTMP1, rTMP1, rTMP3
+ cntlzd rTMP1, rTMP1 /* Count bits not in the mask. */
+ subf rTMP3, rRTN, rSTR
+ subfic rTMP1, rTMP1, 64-7
+ srdi rTMP1, rTMP1, 3
+ add rRTN, rTMP1, rTMP3
+ blr
+
+L(done1):
+ addi rTMP3, rTMP1, -1
+ andc rTMP3, rTMP3, rTMP1
+ cntlzd rTMP3, rTMP3
+ subf rTMP1, rRTN, rSTR
+ subfic rTMP3, rTMP3, 64-7-64
+ sradi rTMP3, rTMP3, 3
+ add rRTN, rTMP1, rTMP3
+ blr
+#endif
+
END (BP_SYM (strlen))
libc_hidden_builtin_def (strlen)