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Avoid casts from unsigned long to floating-point 

Old Microsoft compilers do not support those casts.
This commit is contained in:
Roberto Ierusalimschy 2023-09-08 11:34:39 -03:00
parent 07a9eab23a
commit edd8589f47
1 changed files with 24 additions and 7 deletions
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31
lmathlib.c
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@ -249,6 +249,15 @@ static int math_type (lua_State *L) {
** ===================================================================
*/
/*
** This code uses lots of shifts. ANSI C does not allow shifts greater
** than or equal to the width of the type being shifted, so some shifts
** are written in convoluted ways to match that restriction. For
** preprocessor tests, it assumes a width of 32 bits, so the maximum
** shift there is 31 bits.
*/
/* number of binary digits in the mantissa of a float */
#define FIGS l_floatatt(MANT_DIG)
@ -271,16 +280,19 @@ static int math_type (lua_State *L) {
/* 'long' has at least 64 bits */
#define Rand64 unsigned long
#define SRand64 long
#elif !defined(LUA_USE_C89) && defined(LLONG_MAX)
/* there is a 'long long' type (which must have at least 64 bits) */
#define Rand64 unsigned long long
#define SRand64 long long
#elif ((LUA_MAXUNSIGNED >> 31) >> 31) >= 3
/* 'lua_Unsigned' has at least 64 bits */
#define Rand64 lua_Unsigned
#define SRand64 lua_Integer
#endif
@ -319,23 +331,30 @@ static Rand64 nextrand (Rand64 *state) {
}
/* must take care to not shift stuff by more than 63 slots */
/*
** Convert bits from a random integer into a float in the
** interval [0,1), getting the higher FIG bits from the
** random unsigned integer and converting that to a float.
** Some old Microsoft compilers cannot cast an unsigned long
** to a floating-point number, so we use a signed long as an
** intermediary. When lua_Number is float or double, the shift ensures
** that 'sx' is non negative; in that case, a good compiler will remove
** the correction.
*/
/* must throw out the extra (64 - FIGS) bits */
#define shift64_FIG (64 - FIGS)
/* to scale to [0, 1), multiply by scaleFIG = 2^(-FIGS) */
/* 2^(-FIGS) == 2^-1 / 2^(FIGS-1) */
#define scaleFIG (l_mathop(0.5) / ((Rand64)1 << (FIGS - 1)))
static lua_Number I2d (Rand64 x) {
return (lua_Number)(trim64(x) >> shift64_FIG) * scaleFIG;
SRand64 sx = (SRand64)(trim64(x) >> shift64_FIG);
lua_Number res = (lua_Number)(sx) * scaleFIG;
if (sx < 0)
res += 1.0; /* correct the two's complement if negative */
lua_assert(0 <= res && res < 1);
return res;
}
/* convert a 'Rand64' to a 'lua_Unsigned' */
@ -471,8 +490,6 @@ static lua_Number I2d (Rand64 x) {
#else /* 32 < FIGS <= 64 */
/* must take care to not shift stuff by more than 31 slots */
/* 2^(-FIGS) = 1.0 / 2^30 / 2^3 / 2^(FIGS-33) */
#define scaleFIG \
(l_mathop(1.0) / (UONE << 30) / l_mathop(8.0) / (UONE << (FIGS - 33)))