more efficient hash for numbers in IEEE754 machines

1 files changed, 10 insertions, 9 deletions

diff --git a/llimits.h b/llimits.h
index 9b7a2544..2c69ce53 100644
--- a/llimits.h
+++ b/llimits.h
@@ -1,5 +1,5 @@
 /*
-** $Id: llimits.h,v 1.84 2010/11/08 16:33:20 roberto Exp roberto $
+** $Id: llimits.h,v 1.85 2010/12/10 13:40:22 roberto Exp roberto $
 ** Limits, basic types, and some other `installation-dependent' definitions
 ** See Copyright Notice in lua.h
 */
@@ -174,6 +174,9 @@ typedef lu_int32 Instruction;
 ** lua_number2integer is a macro to convert lua_Number to lua_Integer.
 ** lua_number2unsigned is a macro to convert a lua_Number to a lua_Unsigned.
 ** lua_unsigned2number is a macro to convert a lua_Unsigned to a lua_Number.
+** luai_hashnum is a macro to hash a lua_Number value into an integer.
+** The hash must be deterministic and give reasonable values for
+** both small and large values (outside the range of integers).
 */
 
 #if defined(MS_ASMTRICK)        /* { */
@@ -204,6 +207,10 @@ union luai_Cast { double l_d; LUA_INT32 l_p[2]; };
     volatile union luai_Cast u; u.l_d = (n) + 6755399441055744.0; \
     (i) = (t)u.l_p[LUA_IEEEENDIAN]; }
 
+#define luai_hashnum(i,n)  \
+  { volatile union luai_Cast u; u.l_d = (n) + 1.0;  /* avoid -0 */ \
+    (i) = u.l_p[0] + u.l_p[1]; }  /* add double bits for his hash */
+
 #define lua_number2int(i,n)             lua_number2int32(i, n, int)
 #define lua_number2integer(i,n)         lua_number2int32(i, n, lua_Integer)
 #define lua_number2unsigned(i,n)        lua_number2int32(i, n, lua_Unsigned)
@@ -242,14 +249,8 @@ union luai_Cast { double l_d; LUA_INT32 l_p[2]; };
 #endif
 
 
-/*
-** luai_hashnum is a macro do hash a lua_Number value into an integer.
-** The hash must be deterministic and give reasonable values for
-** both small and large values (outside the range of integers).
-** It is used only in ltable.c.
-*/
 
-#if !defined(luai_hashnum)      /* { */
+#if defined(ltable_c) && !defined(luai_hashnum)         /* { */
 
 #include <float.h>
 #include <math.h>
@@ -258,7 +259,7 @@ union luai_Cast { double l_d; LUA_INT32 l_p[2]; };
   n = frexp(n, &e) * (lua_Number)(INT_MAX - DBL_MAX_EXP);  \
   lua_number2int(i, n); i += e; }
 
-#endif                                          /* } */
+#endif                                                  /* } */