On Fri, Sep 28, 2012 at 5:48 PM, Gabriel Gonzalez <gabriel.gonzalez.gar...@gmail.com> wrote: > This version for ARM improves performance mainly unrolling the loop for > iterations > and reducing the instructions need to look for the null character. > A deeper analysis of this can be found at > http://www.gabrielgonzalezgarcia.com/2012/10/02/mystrlen-vs-android-bionics-strlen-on-arm-cpu/ > where you can find some data which back up the performance improvement. > I have only tested it on a little endian CPU so the BIG ENDIAN chunk might > need some testing > > Signed-off-by: Gabriel Gonzalez <gabriel.gonzalez.gar...@gmail.com> > --- > libc/string/arm/strlen.S | 123 > +++++++++++++++++++++++++++------------------- > 1 file changed, 72 insertions(+), 51 deletions(-) > > diff --git a/libc/string/arm/strlen.S b/libc/string/arm/strlen.S > index 949e918..b87fbb4 100644 > --- a/libc/string/arm/strlen.S > +++ b/libc/string/arm/strlen.S > @@ -46,63 +46,84 @@ strlen: > bx lr > #else > strlen: > - bic r1, r0, $3 @ addr of word containing first byte > - ldr r2, [r1], $4 @ get the first word > - ands r3, r0, $3 @ how many bytes are duff? > - rsb r0, r3, $0 @ get - that number into counter. > - beq Laligned @ skip into main check routine if no > - @ more > -#if __BYTE_ORDER == __BIG_ENDIAN > - orr r2, r2, $0xff000000 @ set this byte to non-zero > - subs r3, r3, $1 @ any more to do? > - IT(t, gt) > - orrgt r2, r2, $0x00ff0000 @ if so, set this byte > - subs r3, r3, $1 @ more? > - IT(t, gt) > - orrgt r2, r2, $0x0000ff00 @ then set. > -#else > - orr r2, r2, $0x000000ff @ set this byte to non-zero > - subs r3, r3, $1 @ any more to do? > - IT(t, gt) > - orrgt r2, r2, $0x0000ff00 @ if so, set this byte > - subs r3, r3, $1 @ more? > - IT(t, gt) > - orrgt r2, r2, $0x00ff0000 @ then set. > -#endif > -Laligned: @ here, we have a word in r2. Does it > - tst r2, $0x000000ff @ contain any zeroes? > - IT(tttt, ne) > - tstne r2, $0x0000ff00 @ > - tstne r2, $0x00ff0000 @ > - tstne r2, $0xff000000 @ > - addne r0, r0, $4 @ if not, the string is 4 bytes longer > - IT(t, ne) > - ldrne r2, [r1], $4 @ and we continue to the next word > - bne Laligned @ > -Llastword: @ drop through to here once we find a > + stmfd sp!, {v1, v2, v3, v4, v5, v6, v7, lr} > + > + mov v7, a1 > + ldr v6, =0x80808080 > + > + ## > + ## un-aligned address till we get aligned > + ## > +1: tst v7, #3 > + beq 0f > + ldrb v1, [v7], #1 > + tst v1, #0xFF > + beq 4f > + bal 1b > + > + > + ## un-rolling strings > + ## as few instructions in the loop > + ## as possible > + ## - Check whether any position equals 0 > +0: ldmfd v7!, {v1, v2, v3, v4} > + sub v5, v1, v6, LSR #7 > + and v5, v5, v6 > + bics v5, v5, v1 > + bne 1f > + sub v5, v2, v6, LSR #7 > + and v5, v5, v6 > + bics v5, v5, v2 > + bne 2f > + sub v5, v3, v6, LSR #7 > + and v5, v5, v6 > + bics v5, v5, v3 > + bne 3f > + sub v5, v4, v6, LSR #7 > + and v5, v5, v6 > + bics v5, v5, v4 > + bne 4f > + beq 0b > + > +4: mov v1, v4 > + bal 0f > +3: mov v1, v3 > + sub v7, v7, #4 > + bal 0f > +2: mov v1, v2 > + sub v7, v7, #8 > + bal 0f > +1: sub v7, v7, #12 > + ## After the loop we calculate the diff > + ## between the end and the begining of the str > + ## > #if __BYTE_ORDER == __BIG_ENDIAN > - tst r2, $0xff000000 @ word that has a zero byte in it > - IT(tttt, ne) > - addne r0, r0, $1 @ > - tstne r2, $0x00ff0000 @ and add up to 3 bytes on to it > - addne r0, r0, $1 @ > - tstne r2, $0x0000ff00 @ (if first three all non-zero, 4th > - IT(t, ne) > - addne r0, r0, $1 @ must be zero) > +0: tst v1, #0xFF000000 > + subeq v7, v7, #1 > + tst v1, #0x00FF0000 > + subeq v7, v7, #1 > + tst v1, #0x0000FF00 > + subeq v7, v7, #1 > + tst v1, #0x000000FF > +4: subeq v7, v7, #1 > #else > - tst r2, $0x000000ff @ > - IT(tttt, ne) > - addne r0, r0, $1 @ > - tstne r2, $0x0000ff00 @ and add up to 3 bytes on to it > - addne r0, r0, $1 @ > - tstne r2, $0x00ff0000 @ (if first three all non-zero, 4th > - IT(t, ne) > - addne r0, r0, $1 @ must be zero) > +0: tst v1, #0xFF > + subeq v7, v7, #1 > + tst v1, #0xFF00 > + subeq v7, v7, #1 > + tst v1, #0xFF0000 > + subeq v7, v7, #1 > + tst v1, #0xFF000000 > +4: subeq v7, v7, #1 > #endif > + > + sub a1, v7, a1 > + > #if defined(__USE_BX__) > + ldmfd sp!, {v1, v2, v3, v4, v5, v6, v7, lr} > bx lr > #else > - mov pc,lr > + ldmfd sp!, {v1, v2, v3, v4, v5, v6, v7, pc} > #endif > #endif > > -- > 1.7.9.5
This looks good. I would like that people try it on various arm's and give it a good test. Current algorithm may be suboptimal but it has been time tested. _______________________________________________ uClibc mailing list uClibc@uclibc.org http://lists.busybox.net/mailman/listinfo/uclibc
