From edd8589f478e784bb8d1a8e9a3bb2bb3ca51738c Mon Sep 17 00:00:00 2001 From: Roberto Ierusalimschy Date: Fri, 8 Sep 2023 11:34:39 -0300 Subject: Avoid casts from unsigned long to floating-point Old Microsoft compilers do not support those casts. --- lmathlib.c | 31 ++++++++++++++++++++++++------- 1 file changed, 24 insertions(+), 7 deletions(-) diff --git a/lmathlib.c b/lmathlib.c index d0b1e1e5..f140d623 100644 --- a/lmathlib.c +++ b/lmathlib.c @@ -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))) -- cgit v1.2.3-55-g6feb