[PATCH] newlib: libc: Improved the readability of strpbrk with minor optimization

[Xiao Zeng]

As mentioned in [PATCH] newlib: libc: Improved the readability of strcspn with minor optimization: <https://sourceware.org/pipermail/newlib/2023/020766.html>

This patch did the same thing and passed the testcases.

Similarly, provide a comparison of risc-v assembly:

no-patch:
---------------------------------------------------------
libc_a-strpbrk.o:     file format elf64-littleriscv


Disassembly of section .text:

0000000000000000 <strpbrk>:
   0:   00054683                lbu     a3,0(a0)

0000000000000004 <.LVL1>:
   4:   06068463                beqz    a3,6c <.L8>
   8:   0005c603                lbu     a2,0(a1)

000000000000000c <.LVL2>:
   c:   02060e63                beqz    a2,48 <.L14>

0000000000000010 <.L6>:
  10:   00058713                mv      a4,a1
  14:   00060793                mv      a5,a2

0000000000000018 <.L5>:
  18:   00f68e63                beq     a3,a5,34 <.L4>
  1c:   00174783                lbu     a5,1(a4)
  20:   00170713                addi    a4,a4,1

0000000000000024 <.LVL4>:
  24:   fe079ae3                bnez    a5,18 <.L5>
  28:   00154683                lbu     a3,1(a0)
  2c:   00150513                addi    a0,a0,1

0000000000000030 <.LVL5>:
  30:   fe0690e3                bnez    a3,10 <.L6>

0000000000000034 <.L4>:
  34:   00074783                lbu     a5,0(a4)
  38:   00f037b3                snez    a5,a5
  3c:   40f007b3                neg     a5,a5
  40:   00f57533                and     a0,a0,a5
  44:   00008067                ret

0000000000000048 <.L14>:
  48:   00154683                lbu     a3,1(a0)
  4c:   00150513                addi    a0,a0,1

0000000000000050 <.LVL8>:
  50:   fe069ce3                bnez    a3,48 <.L14>
  54:   00058713                mv      a4,a1
  58:   00074783                lbu     a5,0(a4)
  5c:   00f037b3                snez    a5,a5
  60:   40f007b3                neg     a5,a5
  64:   00f57533                and     a0,a0,a5

0000000000000068 <.LVL9>:
  68:   00008067                ret

000000000000006c <.L8>:
  6c:   00000513                li      a0,0

0000000000000070 <.LVL11>:
  70:   00008067                ret
---------------------------------------------------------

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>
---------------------------------------------------------
After careful comparison, it was found that there are fewer assembly
instructions after the patch.

2023-12-20 14:10  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