From: Jeff Johnston <jjohnstn@redhat.com>
To: Xiao Zeng <zengxiao@eswincomputing.com>
Cc: "newlib@sourceware.org" <newlib@sourceware.org>,
"palmer@rivosinc.com" <palmer@rivosinc.com>,
jeffreyalaw <jeffreyalaw@gmail.com>,
Torbjorn SVENSSON <torbjorn.svensson@foss.st.com>
Subject: Re: Re: [PATCH] newlib: libc: Improved the readability of strpbrk with minor optimization
Date: Thu, 21 Dec 2023 14:05:29 -0500 [thread overview]
Message-ID: <CAOox84tuPPEvAX3zrQ4N3gGcq_ONdLg7hwpbeub_8z8xyCRK+A@mail.gmail.com> (raw)
In-Reply-To: <202312210916074865474@eswincomputing.com>
[-- Attachment #1: Type: text/plain, Size: 5704 bytes --]
Patch merged. Thanks.
-- Jeff J.
On Wed, Dec 20, 2023 at 8:16 PM Xiao Zeng <zengxiao@eswincomputing.com>
wrote:
> 2023-12-21 06:48 Jeff Johnston <jjohnstn@redhat.com> wrote:
> >
>
> >Unless I am missing something, I think the code could be made even simpler
> >to return the pointer when found and return NULL otherwise.
> Yes, you have found a more efficient method.
> After my testing, fewer assembly instructions were generated. This is
> really exciting.
>
> Xiao's patch:
> ---------------------------------------------------------
> libc_a-strpbrk.o: file format elf64-littleriscv
>
>
> Disassembly of section .text:
>
> 0000000000000000 <strpbrk>:
> 0: 00054683 lbu a3,0(a0)
>
> 0000000000000004 <.LVL1>:
> 4: 04068063 beqz a3,44 <.L10>
> 8: 0005c603 lbu a2,0(a1)
> c: 04060063 beqz a2,4c <.L14>
>
> 0000000000000010 <.L5>:
> 10: 00058793 mv a5,a1
> 14: 00060713 mv a4,a2
> 18: 00c0006f j 24 <.L4>
>
> 000000000000001c <.L17>:
> 1c: 0007c703 lbu a4,0(a5)
> 20: 00070863 beqz a4,30 <.L16>
>
> 0000000000000024 <.L4>:
> 24: 00178793 addi a5,a5,1
>
> 0000000000000028 <.LVL5>:
> 28: fee69ae3 bne a3,a4,1c <.L17>
>
> 000000000000002c <.L1>:
> 2c: 00008067 ret
>
> 0000000000000030 <.L16>:
> 30: 00154683 lbu a3,1(a0)
> 34: 00150513 addi a0,a0,1
>
> 0000000000000038 <.LVL8>:
> 38: fc069ce3 bnez a3,10 <.L5>
>
> 000000000000003c <.L6>:
> 3c: 0007c783 lbu a5,0(a5)
>
> 0000000000000040 <.LVL9>:
> 40: fe0796e3 bnez a5,2c <.L1>
>
> 0000000000000044 <.L10>:
> 44: 00000513 li a0,0
>
> 0000000000000048 <.LVL11>:
> 48: 00008067 ret
>
> 000000000000004c <.L14>:
> 4c: 00154683 lbu a3,1(a0)
> 50: 00150513 addi a0,a0,1
> 54: fe069ce3 bnez a3,4c <.L14>
> 58: 00058793 mv a5,a1
> 5c: fe1ff06f j 3c <.L6>
> ---------------------------------------------------------
>
> Jeff's patch
> ---------------------------------------------------------
> libc_a-strpbrk.o: file format elf64-littleriscv
>
>
> Disassembly of section .text:
>
> 0000000000000000 <strpbrk>:
> 0: 00054683 lbu a3,0(a0)
> 4: 02068c63 beqz a3,3c <.L8>
> 8: 0005c603 lbu a2,0(a1)
> c: 02060c63 beqz a2,44 <.L12>
>
> 0000000000000010 <.L5>:
> 10: 00058793 mv a5,a1
> 14: 00060713 mv a4,a2
> 18: 00c0006f j 24 <.L4>
>
> 000000000000001c <.L15>:
> 1c: 0007c703 lbu a4,0(a5)
> 20: 00070863 beqz a4,30 <.L14>
>
> 0000000000000024 <.L4>:
> 24: 00178793 addi a5,a5,1
>
> 0000000000000028 <.LVL4>:
> 28: fed71ae3 bne a4,a3,1c <.L15>
> 2c: 00008067 ret
>
> 0000000000000030 <.L14>:
> 30: 00154683 lbu a3,1(a0)
> 34: 00150513 addi a0,a0,1
>
> 0000000000000038 <.LVL6>:
> 38: fc069ce3 bnez a3,10 <.L5>
>
> 000000000000003c <.L8>:
> 3c: 00000513 li a0,0
>
> 0000000000000040 <.LVL7>:
> 40: 00008067 ret
>
> 0000000000000044 <.L12>:
> 44: 00154683 lbu a3,1(a0)
> 48: 00150513 addi a0,a0,1
> 4c: fe069ce3 bnez a3,44 <.L12>
> 50: fedff06f j 3c <.L8>
> ---------------------------------------------------------
> After careful comparison, it was found that there are fewer assembly
> instructions after the Jeff's patch.
>
> >
> >index 774db1e..d984745 100644
> >--- a/newlib/libc/string/strpbrk.c
> >+++ b/newlib/libc/string/strpbrk.c
> >@@ -29,23 +29,16 @@ strpbrk (const char *s1,
> > const char *s2)
> > {
> > const char *c = s2;
> >- if (!*s1)
> >- return (char *) NULL;
> >
> > while (*s1)
> > {
> > for (c = s2; *c; c++)
> > {
> > if (*s1 == *c)
> >- break;
> >+ return (char *) s1;
> > }
> >- if (*c)
> >- break;
> > s1++;
> > }
> >
> >- if (*c == '\0')
> >- s1 = NULL;
> >-
> >- return (char *) s1;
> >+ return (char *) NULL;
> > }
> >
> >On Wed, Dec 20, 2023 at 1:12 AM Xiao Zeng <zengxiao@eswincomputing.com>
> >wrote:
> >
> >> Signed-off-by: Xiao Zeng <zengxiao@eswincomputing.com>
> >> ---
> >> newlib/libc/string/strpbrk.c | 5 ++---
> >> 1 file changed, 2 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/newlib/libc/string/strpbrk.c b/newlib/libc/string/strpbrk.c
> >> index 774db1e6d..95e89c20c 100644
> >> --- a/newlib/libc/string/strpbrk.c
> >> +++ b/newlib/libc/string/strpbrk.c
> >> @@ -37,15 +37,14 @@ strpbrk (const char *s1,
> >> for (c = s2; *c; c++)
> >> {
> >> if (*s1 == *c)
> >> - break;
> >> + goto end;
> >> }
> >> - if (*c)
> >> - break;
> >> s1++;
> >> }
> >>
> >> if (*c == '\0')
> >> s1 = NULL;
> >>
> >> +end:
> >> return (char *) s1;
> >> }
> >> --
> >> 2.17.1
> >>
> >>
>
> Thanks
> Xiao Zeng
>
>
next prev parent reply other threads:[~2023-12-21 19:05 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-20 6:10 Xiao Zeng
2023-12-20 6:25 ` Xiao Zeng
2023-12-20 22:48 ` Jeff Johnston
2023-12-21 1:16 ` Xiao Zeng
2023-12-21 19:05 ` Jeff Johnston [this message]
2023-12-22 1:21 ` Xiao Zeng
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