Re: [PATCH 01/12] Make starts_with() a wrapper of skip_prefix()

[Junio C Hamano]

Nguyễn Thái Ngọc Duy  pclo...@gmail.com writes:

 starts_with() started out as a copy of prefixcmp(). But if we don't
 care about the sorting order, the logic looks closer to
 skip_prefix(). This looks like a good thing to do.

 Signed-off-by: Nguyễn Thái Ngọc Duy pclo...@gmail.com
 ---

Sure, but the implementation of skip_prefix() scans the prefix
string twice, while prefixcmp() aka starts_with() does it only once.

I'd expect a later step in this series would rectify this micro
regression in the performance, though ;-)

  git-compat-util.h | 6 +-
  strbuf.c  | 9 -
  2 files changed, 5 insertions(+), 10 deletions(-)

 diff --git a/git-compat-util.h b/git-compat-util.h
 index b73916b..84f1078 100644
 --- a/git-compat-util.h
 +++ b/git-compat-util.h
 @@ -350,7 +350,6 @@ extern void set_die_routine(NORETURN_PTR void 
 (*routine)(const char *err, va_lis
  extern void set_error_routine(void (*routine)(const char *err, va_list 
 params));
  extern void set_die_is_recursing_routine(int (*routine)(void));
  
 -extern int starts_with(const char *str, const char *prefix);
  extern int prefixcmp(const char *str, const char *prefix);
  extern int ends_with(const char *str, const char *suffix);
  extern int suffixcmp(const char *str, const char *suffix);
 @@ -361,6 +360,11 @@ static inline const char *skip_prefix(const char *str, 
 const char *prefix)
   return strncmp(str, prefix, len) ? NULL : str + len;
  }
  
 +static inline int starts_with(const char *str, const char *prefix)
 +{
 + return skip_prefix(str, prefix) != NULL;
 +}
 +
  #if defined(NO_MMAP) || defined(USE_WIN32_MMAP)
  
  #ifndef PROT_READ
 diff --git a/strbuf.c b/strbuf.c
 index 83caf4a..bd4c0d8 100644
 --- a/strbuf.c
 +++ b/strbuf.c
 @@ -1,15 +1,6 @@
  #include cache.h
  #include refs.h
  
 -int starts_with(const char *str, const char *prefix)
 -{
 - for (; ; str++, prefix++)
 - if (!*prefix)
 - return 1;
 - else if (*str != *prefix)
 - return 0;
 -}
 -
  int prefixcmp(const char *str, const char *prefix)
  {
   for (; ; str++, prefix++)
--
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Re: [PATCH 01/12] Make starts_with() a wrapper of skip_prefix()

[Junio C Hamano]

Junio C Hamano gits...@pobox.com writes:

 Nguyễn Thái Ngọc Duy  pclo...@gmail.com writes:

 starts_with() started out as a copy of prefixcmp(). But if we don't
 care about the sorting order, the logic looks closer to
 skip_prefix(). This looks like a good thing to do.

 Signed-off-by: Nguyễn Thái Ngọc Duy pclo...@gmail.com
 ---

 Sure, but the implementation of skip_prefix() scans the prefix
 string twice, while prefixcmp() aka starts_with() does it only once.

 I'd expect a later step in this series would rectify this micro
 regression in the performance, though ;-)

... and I did not see one, but it would be trivial on top.

 git-compat-util.h | 7 +--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/git-compat-util.h b/git-compat-util.h
index b72a80d..59265af 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -356,8 +356,11 @@ extern int suffixcmp(const char *str, const char *suffix);
 
 static inline const char *skip_prefix_defval(const char *str, const char 
*prefix, const char *defval)
 {
-   size_t len = strlen(prefix);
-   return strncmp(str, prefix, len) ? defval : str + len;
+   for ( ; ; str++, prefix++)
+   if (!*prefix)
+   return str;
+   else if (*str != *prefix)
+   return defval;
 }
 
 static inline const char *skip_prefix(const char *str, const char *prefix)
--
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