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.

1 files changed, 21 insertions, 21 deletions

diff --git a/src/character.h b/src/character.h
index d4d77504426..af5023f77cc 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;
                     }
                 }
             }