Changeset 98495 in webkit

Timestamp:

Oct 26, 2011, 10:12:13 AM (15 years ago)

Author:

msaboff@apple.com

Message:

Increase StringImpl Flag Bits for 8 bit Strings
​https://bugs.webkit.org/show_bug.cgi?id=70937

Increased the number of bits used for flags in StringImpl
from 6 to 8 bits. This frees up 2 flag bits that will be
used for 8-bit string support. Updated hash methods accordingly.
Changed hash value masking from the low bits to the high
bits.

Reviewed by Darin Adler.

Source/JavaScriptCore:

• create_hash_table:
• wtf/StringHasher.h:

(WTF::StringHasher::hash):

• wtf/text/StringImpl.h:

Source/WebCore:

• bindings/scripts/CodeGeneratorJS.pm:

(GenerateHashValue):

Location:

trunk/Source

Files:

• JavaScriptCore/ChangeLog (modified) (1 diff)
• JavaScriptCore/create_hash_table (modified) (2 diffs)
• JavaScriptCore/wtf/StringHasher.h (modified) (2 diffs)
• JavaScriptCore/wtf/text/StringImpl.h (modified) (1 diff)
• WebCore/ChangeLog (modified) (1 diff)
• WebCore/bindings/scripts/CodeGeneratorJS.pm (modified) (2 diffs)

trunk/Source/JavaScriptCore/ChangeLog

@@ +1 @@
+2011-10-26  Michael Saboff  <msaboff@apple.com>
+
+        Increase StringImpl Flag Bits for 8 bit Strings
+        https://bugs.webkit.org/show_bug.cgi?id=70937
+
+        Increased the number of bits used for flags in StringImpl
+        from 6 to 8 bits. This frees up 2 flag bits that will be
+        used for 8-bit string support. Updated hash methods accordingly.
+        Changed hash value masking from the low bits to the high
+        bits.
+
+        Reviewed by Darin Adler.
+
+        * create_hash_table:
+        * wtf/StringHasher.h:
+        (WTF::StringHasher::hash):
+        * wtf/text/StringImpl.h:
+
 2011-10-26  Dan Bernstein  <mitz@apple.com>
 

trunk/Source/JavaScriptCore/create_hash_table

@@ -222 +222 @@
   $hash ^= (leftShift($hash, 10)% $EXP2_32);
 
-  # Save 6 bits for StringImpl to use as flags.
-  $hash = ($hash >> 6);
+  # Save 8 bits for StringImpl to use as flags.
+  $hash &= 0xffffff;
 
   # This avoids ever returning a hash code of 0, since that is used to
@@ -229 +229 @@
   # reasonable fidelity to a hash code of 0 because it is likely to yield
   # exactly 0 when hash lookup masks out the high bits.
-  $hash = (0x80000000 >> 6) if ($hash == 0);
+  $hash = (0x80000000 >> 8) if ($hash == 0);
 
   return $hash;

trunk/Source/JavaScriptCore/wtf/StringHasher.h

@@ -37 +37 @@
 class StringHasher {
 public:
-    static const unsigned flagCount = 6; // Save 6 bits for StringImpl to use as flags.
+    static const unsigned flagCount = 8; // Save 8 bits for StringImpl to use as flags.
 
     inline StringHasher()
@@ -82 +82 @@
         result ^= result << 10;
 
-        // Reserving the high bits for flags preserves most of the hash's value,
-        // since hash lookup typically masks out the high bits anyway.
-        result >>= flagCount;
+        // Reserving space from the high bits for flags preserves most of the hash's
+        // value, since hash lookup typically masks out the high bits anyway.
+        result &= (1u << (sizeof(result) * 8 - flagCount)) - 1;
 
         // This avoids ever returning a hash code of 0, since that is used to

trunk/Source/JavaScriptCore/wtf/text/StringImpl.h

@@ -382 +382 @@
     static const unsigned s_refCountIncrement = 0x2; // This allows us to ref / deref without disturbing the static string flag.
 
-    // The bottom 6 bits in the hash are flags.
-    static const unsigned s_flagCount = 6;
+    // The bottom 8 bits in the hash are flags.
+    static const unsigned s_flagCount = 8;
     static const unsigned s_flagMask = (1u << s_flagCount) - 1;
     COMPILE_ASSERT(s_flagCount == StringHasher::flagCount, StringHasher_reserves_enough_bits_for_StringImpl_flags);

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2011-10-26  Michael Saboff  <msaboff@apple.com>
+
+        Increase StringImpl Flag Bits for 8 bit Strings
+        https://bugs.webkit.org/show_bug.cgi?id=70937
+
+        Increased the number of bits used for flags in StringImpl
+        from 6 to 8 bits. This frees up 2 flag bits that will be
+        used for 8-bit string support. Updated hash methods accordingly.
+        Changed hash value masking from the low bits to the high
+        bits.
+
+        Reviewed by Darin Adler.
+
+        * bindings/scripts/CodeGeneratorJS.pm:
+        (GenerateHashValue):
+
 2011-10-26  Dimitri Glazkov  <dglazkov@chromium.org>
 

trunk/Source/WebCore/bindings/scripts/CodeGeneratorJS.pm

@@ -3069 +3069 @@
     $hash ^= (leftShift($hash, 10)% $EXP2_32);
     
-    # Save 6 bits for StringImpl to use as flags.
-    $hash = ($hash >> 6);
+    # Save 8 bits for StringImpl to use as flags.
+    $hash &= 0xffffff;
     
     # This avoids ever returning a hash code of 0, since that is used to
@@ -3076 +3076 @@
     # reasonable fidelity to a hash code of 0 because it is likely to yield
     # exactly 0 when hash lookup masks out the high bits.
-    $hash = (0x80000000 >> 6) if ($hash == 0);
+    $hash = (0x80000000 >> 8) if ($hash == 0);
     
     return $hash;