master e49d3a4: Improve multibyte_length performance

[Paul Eggert]

branch: master
commit e49d3a45cd4a0554aa98c45f0976ed513c500951
Author: Paul Eggert <address@hidden>
Commit: Paul Eggert <address@hidden>

    Improve multibyte_length performance
    
    * src/character.h (multibyte_length):
    Merge tests so that there are fewer conditional branches.
    This improved CPU speed of ‘make compile-always’
    by about 1.5% on my platform.
---
 src/character.h | 42 +++++++++++++++++++++---------------------
 1 file changed, 21 insertions(+), 21 deletions(-)

diff --git a/src/character.h b/src/character.h
index d4d7750..af5023f 100644
--- a/src/character.h
+++ b/src/character.h
@@ -317,30 +317,30 @@ multibyte_length (unsigned char const *p, unsigned char 
const *pend,
        return 1;
       if (!check || p + 1 < pend)
        {
-         /* The 'unsigned int' avoids int overflow in the 5-byte case.  */
-         unsigned int d = p[1];
-
-         if (TRAILING_CODE_P (d))
+         unsigned char d = p[1];
+         int w = ((d & 0xC0) << 2) + c;
+         if ((allow_8bit ? 0x2C0 : 0x2C2) <= w && w <= 0x2DF)
+           return 2;
+         if (!check || p + 2 < pend)
            {
-             if (allow_8bit ? (c & 0xE0) == 0xC0 : 0xC2 <= c && c <= 0xDF)
-               return 2;
-             if ((!check || p + 2 < pend)
-                 && TRAILING_CODE_P (p[2]))
+             unsigned char e = p[2];
+             w += (e & 0xC0) << 4;
+             int w1 = w | ((d & 0x20) >> 2);
+             if (0xAE1 <= w1 && w1 <= 0xAEF)
+               return 3;
+             if (!check || p + 3 < pend)
                {
-                 if ((c & 0xF0) == 0xE0 && ((c & 0x0F) | (d & 0x20)))
-                   return 3;
-                 if ((!check || p + 3 < pend) && TRAILING_CODE_P (p[3]))
+                 unsigned char f = p[3];
+                 w += (f & 0xC0) << 6;
+                 int w2 = w | ((d & 0x30) >> 3);
+                 if (0x2AF1 <= w2 && w2 <= 0x2AF7)
+                   return 4;
+                 if (!check || p + 4 < pend)
                    {
-                     if ((c & 0xF8) == 0xF0 && ((c & 0x07) | (d & 0x30)))
-                       return 4;
-                     if (c == 0xF8 && (!check || p + 4 < pend)
-                         && TRAILING_CODE_P (p[4]))
-                       {
-                         unsigned int w = ((d << 24) + (p[2] << 16)
-                                           + (p[3] << 8) + p[4]);
-                         if (0x88808080 <= w && w <= 0x8FBFBDBF)
-                           return 5;
-                       }
+                     int_fast64_t lw = w + ((p[4] & 0xC0) << 8),
+                       w3 = (lw << 24) + (d << 16) + (e << 8) + f;
+                     if (0xAAF8888080 <= w3 && w3 <= 0xAAF88FBFBD)
+                       return 5;
                    }
                }
            }