/* Optimized strlen implementation for PowerPC64.
- Copyright (C) 1997-2013 Free Software Foundation, Inc.
+ Copyright (C) 1997-2015 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
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).
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
ENTRY (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
#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
dcbt 0,rRTN
clrrdi rSTR, rRTN, 3
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. */
+/* 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. */
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
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 (strlen)
libc_hidden_builtin_def (strlen)
projects / thirdparty / glibc.git / blobdiff