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using unsigned comparison in 'l_intfitsf' (avoids one comparison)

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Roberto Ierusalimschy 2018-04-02 14:52:07 -03:00
parent 8d50a998e3
commit 3d0b5edfe4
1 changed files with 13 additions and 9 deletions
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22
lvm.c
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@ -1,5 +1,5 @@
/* /*
** $Id: lvm.c,v 2.350 2018/03/07 15:55:38 roberto Exp roberto $ ** $Id: lvm.c,v 2.351 2018/03/16 14:21:20 roberto Exp roberto $
** Lua virtual machine ** Lua virtual machine
** See Copyright Notice in lua.h ** See Copyright Notice in lua.h
*/ */
@ -50,24 +50,28 @@
/* /*
** 'l_intfitsf' checks whether a given integer can be converted to a ** 'l_intfitsf' checks whether a given integer is in the range that
** float without rounding. Used in comparisons. ** can be converted to a float without rounding. Used in comparisons.
*/ */
/* number of bits in the mantissa of a float */ /* number of bits in the mantissa of a float */
#define NBM (l_mathlim(MANT_DIG)) #define NBM (l_mathlim(MANT_DIG))
/* /*
** Check whether some integers may not fit in a float, that is, whether ** Check whether some integers may not fit in a float, testing whether
** (maxinteger >> NBM) > 0 (that implies (1 << NBM) <= maxinteger). ** (maxinteger >> NBM) > 0. (That implies (1 << NBM) <= maxinteger.)
** (The shifts are done in parts to avoid shifting by more than the size ** (The shifts are done in parts, to avoid shifting by more than the size
** of an integer. In a worst case, NBM == 113 for long double and ** of an integer. In a worst case, NBM == 113 for long double and
** sizeof(integer) == 32.) ** sizeof(long) == 32.)
*/ */
#if ((((LUA_MAXINTEGER >> (NBM / 4)) >> (NBM / 4)) >> (NBM / 4)) \ #if ((((LUA_MAXINTEGER >> (NBM / 4)) >> (NBM / 4)) >> (NBM / 4)) \
>> (NBM - (3 * (NBM / 4)))) > 0 >> (NBM - (3 * (NBM / 4)))) > 0
#define l_intfitsf(i) \ /* limit for integers that fit in a float */
(-((lua_Integer)1 << NBM) <= (i) && (i) <= ((lua_Integer)1 << NBM)) #define MAXINTFITSF ((lua_Unsigned)1 << NBM)
/* check whether 'i' is in the interval [-MAXINTFITSF, MAXINTFITSF] */
#define l_intfitsf(i) ((MAXINTFITSF + l_castS2U(i)) <= (2 * MAXINTFITSF))
#else /* all integers fit in a float precisely */ #else /* all integers fit in a float precisely */