[PATCH 6/6] scm_i_utf8_string_hash: optimize ASCII

[Rob Browning]

Since we already compute the char length, use that to detect all ASCII
strings and handle those the same way we handle latin-1.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
---
 libguile/hash.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/libguile/hash.c b/libguile/hash.c
index d92f60df8..bc65deb25 100644
--- a/libguile/hash.c
+++ b/libguile/hash.c
@@ -169,25 +169,29 @@ scm_i_latin1_string_hash (const char *str, size_t len)
 unsigned long 
 scm_i_utf8_string_hash (const char *str, size_t len)
 {
-  const uint8_t *end, *ustr = (const uint8_t *) str;
-  unsigned long ret;
-
-  /* The length of the string in characters.  This name corresponds to
-     Jenkins' original name.  */
-  size_t length;
-
-  uint32_t a, b, c, u32;
-
   if (len == (size_t) -1)
     len = strlen (str);
 
-  end = ustr + len;
-
+  const uint8_t *ustr = (const uint8_t *) str;
   if (u8_check (ustr, len) != NULL)
     /* Invalid UTF-8; punt.  */
     return scm_i_string_hash (scm_from_utf8_stringn (str, len));
 
-  length = u8_mbsnlen (ustr, len);
+  /* The length of the string in characters.  This name corresponds to
+     Jenkins' original name.  */
+  size_t length = u8_mbsnlen (ustr, len);
+
+  if (len == length) // ascii, same as narrow_string_hash above
+    {
+      unsigned long ret;
+      JENKINS_LOOKUP3_HASHWORD2 (str, len, ret);
+      ret >>= 2; /* Ensure that it fits in a fixnum.  */
+      return ret;
+    }
+
+  const uint8_t *end = ustr + len;
+  uint32_t a, b, c, u32;
+  unsigned long ret;
 
   /* Set up the internal state.  */
   a = b = c = 0xdeadbeef + ((uint32_t)(length<<2)) + 47;
-- 
2.43.0