diff options
Diffstat (limited to 'sysdeps/powerpc/powerpc32/strlen.S')
| -rw-r--r-- | sysdeps/powerpc/powerpc32/strlen.S | 69 |
1 files changed, 52 insertions, 17 deletions
diff --git a/sysdeps/powerpc/powerpc32/strlen.S b/sysdeps/powerpc/powerpc32/strlen.S index 9a6eafc382..a7153ed7a2 100644 --- a/sysdeps/powerpc/powerpc32/strlen.S +++ b/sysdeps/powerpc/powerpc32/strlen.S @@ -29,7 +29,12 @@ 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). @@ -72,7 +77,7 @@ ENTRY (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 @@ -82,9 +87,9 @@ ENTRY (strlen) #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 clrrwi rSTR, rRTN, 2 @@ -93,15 +98,20 @@ ENTRY (strlen) 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 @@ -110,11 +120,12 @@ ENTRY (strlen) 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. */ @@ -128,28 +139,52 @@ L(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, 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 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 (strlen) libc_hidden_builtin_def (strlen) |