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Re: some optimizations


On Tue, Oct 17, 2000 at 11:54:03PM -0400, DJ Delorie wrote:
>
>Using static lookup tables instead of arithmetic, shortcutting
>expensive string comparisons, and defering code until it's really
>needed.  Shaves about 1.5% off a ../configure.  Comments?

I think we should be able to get the same strcmp effect by using
__builtin_strcmp.  I'm not sure why I didn't do that to start with.
If that doesn't give us an improvement then maybe an inline function
wrapper around strcmp would hide the initial "*newp == 'T'" strangeness.

The case folding stuff is interesting, though.  We should probably move
the string stuff to a separate string.cc or something, and implement our
own versions of tolower, strlwr, too.  tolower should be an inline function,
of course...

Moving the len calculation in posify is an obvious optimization.
Probably making this an inline function would also allow moving any
tests there.

As I pointed out in private email, the optimizing of environ_init is
not going to save much in the common case since, in 1.1.5, it is
only exercised by the first cygwin process which is started.  After
that an environ array is passed around, just like UNIX.

cgf

>Index: environ.cc
>===================================================================
>RCS file: /cvs/src/src/winsup/cygwin/environ.cc,v
>retrieving revision 1.28
>diff -p -2 -r1.28 environ.cc
>*** environ.cc	2000/10/16 23:55:57	1.28
>--- environ.cc	2000/10/18 03:52:10
>*************** static win_env conv_envvars[] =
>*** 62,65 ****
>--- 62,67 ----
>    };
>  
>+ static unsigned char conv_start_chars[256] = {0};
>+ 
>  void
>  win_env::add_cache (const char *in_posix, const char *in_native)
>*************** win_env * __stdcall
>*** 92,95 ****
>--- 94,100 ----
>  getwinenv (const char *env, const char *in_posix)
>  {
>+   if (!conv_start_chars[(unsigned char)*env])
>+     return NULL;
>+ 
>    for (int i = 0; conv_envvars[i].name != NULL; i++)
>      if (strncasematch (env, conv_envvars[i].name, conv_envvars[i].namelen))
>*************** posify (char **here, const char *value)
>*** 114,118 ****
>    char *src = *here;
>    win_env *conv;
>!   int len = strcspn (src, "=") + 1;
>  
>    if (!(conv = getwinenv (src)))
>--- 119,123 ----
>    char *src = *here;
>    win_env *conv;
>!   int len;
>  
>    if (!(conv = getwinenv (src)))
>*************** posify (char **here, const char *value)
>*** 122,125 ****
>--- 127,132 ----
>       mounted equivalents - if there is one.  */
>  
>+   len = strcspn (src, "=") + 1;
>+ 
>    char *outenv = (char *) malloc (1 + len + conv->posix_len (value));
>    memcpy (outenv, src, len);
>*************** environ_init (char **envp, int envc)
>*** 528,531 ****
>--- 535,549 ----
>    static char cygterm[] = "TERM=cygwin";
>  
>+   static int initted = 0;
>+   if (!initted)
>+     {
>+       for (int i = 0; conv_envvars[i].name != NULL; i++)
>+ 	{
>+ 	  conv_start_chars[tolower(conv_envvars[i].name[0])] = 1;
>+ 	  conv_start_chars[toupper(conv_envvars[i].name[0])] = 1;
>+ 	}
>+       initted = 1;
>+     }
>+ 
>    regopt ("default");
>    if (myself->progname[0])
>*************** environ_init (char **envp, int envc)
>*** 571,579 ****
>        if (!parent_alive)
>  	ucenv (newp, eq);
>!       if (strncmp (newp, "TERM=", 5) == 0)
>  	sawTERM = 1;
>!       if (strncmp (newp, "CYGWIN=", sizeof("CYGWIN=") - 1) == 0)
>  	parse_options (newp + sizeof("CYGWIN=") - 1);
>!       if (*eq)
>  	posify (envp + i, *++eq ? eq : --eq);
>        debug_printf ("%s", envp[i]);
>--- 589,597 ----
>        if (!parent_alive)
>  	ucenv (newp, eq);
>!       if (*newp == 'T' && strncmp (newp, "TERM=", 5) == 0)
>  	sawTERM = 1;
>!       if (*newp == 'C' && strncmp (newp, "CYGWIN=", sizeof("CYGWIN=") - 1) == 0)
>  	parse_options (newp + sizeof("CYGWIN=") - 1);
>!       if (*eq && conv_start_chars[(unsigned char)envp[i][0]])
>  	posify (envp + i, *++eq ? eq : --eq);
>        debug_printf ("%s", envp[i]);
>Index: path.cc
>===================================================================
>RCS file: /cvs/src/src/winsup/cygwin/path.cc,v
>retrieving revision 1.71
>diff -p -2 -r1.71 path.cc
>*** path.cc	2000/10/17 01:46:26	1.71
>--- path.cc	2000/10/18 03:52:11
>*************** cygwin_split_path (const char *path, cha
>*** 2765,2770 ****
>  /********************** String Helper Functions ************************/
>  
>  #define CHXOR ('a' ^ 'A')
>! #define ch_case_eq(ch1, ch2) \
>      ({ \
>        unsigned char x; \
>--- 2765,2789 ----
>  /********************** String Helper Functions ************************/
>  
>+ static char case_folded[] = {
>+    0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,  15,
>+   16,  17,  18,  19,  20,  21,  22,  23,  24,  25,  26,  27,  28,  29,  30,  31,
>+   32, '!', '"', '#', '$', '%', '&',  39, '(', ')', '*', '+', ',', '-', '.', '/',
>+  '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?',
>+  '@', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
>+  'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '[',  92, ']', '^', '_',
>+  '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
>+  'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '{', '|', '}', '~', 127,
>+  128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143,
>+  144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159,
>+  160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175,
>+  176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191,
>+  192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207,
>+  208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223,
>+  224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239,
>+  240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255
>+ };
>+ 
>  #define CHXOR ('a' ^ 'A')
>! #define old_ch_case_eq(ch1, ch2) \
>      ({ \
>        unsigned char x; \
>*************** cygwin_split_path (const char *path, cha
>*** 2772,2775 ****
>--- 2791,2798 ----
>         (x != CHXOR || !isalpha (ch1))); \
>      })
>+ 
>+ // This is about 10% faster than the above logic, on average
>+ #define ch_case_eq(ch1, ch2) (case_folded[(unsigned char)(ch1)] \
>+ 				== case_folded[(unsigned char)(ch2)])
>  
>  /* Return TRUE if two strings match up to length n */

-- 
cgf@cygnus.com                        Red Hat, Inc.
http://sources.redhat.com/            http://www.redhat.com/

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