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

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

[Xiao Zeng]

Signed-off-by: Xiao Zeng <zengxiao@eswincomputing.com>
---
 newlib/libc/string/strspn.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/newlib/libc/string/strspn.c b/newlib/libc/string/strspn.c
index baf239947..9d46ce2eb 100644
--- a/newlib/libc/string/strspn.c
+++ b/newlib/libc/string/strspn.c
@@ -41,10 +41,11 @@ strspn (const char *s1,
       for (c = s2; *c; c++)
 	{
 	  if (*s1 == *c)
-	    break;
+	    goto end;
 	}
       if (*c == '\0')
 	break;
+end:
       s1++;
     }
 
-- 
2.17.1

Re: [PATCH] newlib: libc: Improved the readability of strspn 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-strspn.o:     file format elf64-littleriscv


Disassembly of section .text:

0000000000000000 <strspn>:
   0:   00054683                lbu     a3,0(a0)
   4:   00050893                mv      a7,a0

0000000000000008 <.LVL1>:
   8:   04068463                beqz    a3,50 <.L6>
   c:   0005c803                lbu     a6,0(a1)

0000000000000010 <.LVL2>:
  10:   00000513                li      a0,0

0000000000000014 <.LVL3>:
  14:   00081463                bnez    a6,1c <.L13>
  18:   00008067                ret

000000000000001c <.L13>:
  1c:   00088613                mv      a2,a7

0000000000000020 <.L5>:
  20:   00058793                mv      a5,a1
  24:   00080713                mv      a4,a6
  28:   00c0006f                j       34 <.L4>

000000000000002c <.L14>:
  2c:   0007c703                lbu     a4,0(a5)
  30:   00070c63                beqz    a4,48 <.L11>

0000000000000034 <.L4>:
  34:   00178793                addi    a5,a5,1

0000000000000038 <.LVL7>:
  38:   fee69ae3                bne     a3,a4,2c <.L14>
  3c:   00164683                lbu     a3,1(a2)
  40:   00160613                addi    a2,a2,1
  44:   fc069ee3                bnez    a3,20 <.L5>

0000000000000048 <.L11>:
  48:   41160533                sub     a0,a2,a7
  4c:   00008067                ret

0000000000000050 <.L6>:
  50:   00000513                li      a0,0

0000000000000054 <.LVL10>:
  54:   00008067                ret
---------------------------------------------------------

patch
---------------------------------------------------------
libc_a-strspn.o:     file format elf64-littleriscv


Disassembly of section .text:

0000000000000000 <strspn>:
   0:   00054683                lbu     a3,0(a0)
   4:   04068063                beqz    a3,44 <.L11>
   8:   0005c803                lbu     a6,0(a1)

000000000000000c <.LVL1>:
   c:   00050613                mv      a2,a0
  10:   02080a63                beqz    a6,44 <.L11>

0000000000000014 <.L5>:
  14:   00058793                mv      a5,a1
  18:   00080713                mv      a4,a6
  1c:   00c0006f                j       28 <.L6>

0000000000000020 <.L4>:
  20:   0007c703                lbu     a4,0(a5)
  24:   00070c63                beqz    a4,3c <.L12>

0000000000000028 <.L6>:
  28:   00178793                addi    a5,a5,1

000000000000002c <.LVL5>:
  2c:   fee69ae3                bne     a3,a4,20 <.L4>

0000000000000030 <.LDL1>:
  30:   00164683                lbu     a3,1(a2)
  34:   00160613                addi    a2,a2,1
  38:   fc069ee3                bnez    a3,14 <.L5>

000000000000003c <.L12>:
  3c:   40a60533                sub     a0,a2,a0

0000000000000040 <.LVL7>:
  40:   00008067                ret

0000000000000044 <.L11>:
  44:   00000513                li      a0,0

0000000000000048 <.LVL9>:
  48:   00008067                ret
---------------------------------------------------------
After careful comparison, it was found that there are fewer assembly
instructions after the patch.

2023-12-20 14:43  Xiao Zeng <zengxiao@eswincomputing.com> wrote:
>
 
>Signed-off-by: Xiao Zeng <zengxiao@eswincomputing.com>
>---
> newlib/libc/string/strspn.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>diff --git a/newlib/libc/string/strspn.c b/newlib/libc/string/strspn.c
>index baf239947..9d46ce2eb 100644
>--- a/newlib/libc/string/strspn.c
>+++ b/newlib/libc/string/strspn.c
>@@ -41,10 +41,11 @@ strspn (const char *s1,
>       for (c = s2; *c; c++)
> {
>   if (*s1 == *c)
>-	    break;
>+	    goto end;
> }
>       if (*c == '\0')
> break;
>+end:
>       s1++;
>     }
>
>--
>2.17.1
 
Thanks
Xiao Zeng