diff options
Diffstat (limited to 'sal')
| -rw-r--r-- | sal/rtl/math.cxx | 53 |
1 files changed, 52 insertions, 1 deletions
diff --git a/sal/rtl/math.cxx b/sal/rtl/math.cxx index 338f40d1469f..32121b34b2f1 100644 --- a/sal/rtl/math.cxx +++ b/sal/rtl/math.cxx @@ -37,6 +37,10 @@ #include <math.h> #include <stdlib.h> +#if !HAVE_GCC_BUILTIN_FFS && !defined _WIN32 + #include <strings.h> +#endif + static int const n10Count = 16; static double const n10s[2][n10Count] = { { 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, @@ -169,6 +173,47 @@ bool isRepresentableInteger(double fAbsValue) return false; } +// Returns 1-based index of least significant bit in a number, or zero if number is zero +int findFirstSetBit(unsigned n) +{ +#if HAVE_GCC_BUILTIN_FFS + return __builtin_ffs(n); +#elif defined _WIN32 + unsigned long pos; + unsigned char bNonZero = _BitScanForward(&pos, n); + return (bNonZero == 0) ? 0 : pos + 1; +#else + return ffs(n); +#endif +} + +/** Returns number of binary bits for fractional part of the number + Expects a proper non-negative double value, not +-INF, not NAN + */ +int getBitsInFracPart(double fAbsValue) +{ + assert(rtl::math::isFinite(fAbsValue) && fAbsValue >= 0.0); + if (fAbsValue == 0.0) + return 0; + auto pValParts = reinterpret_cast< const sal_math_Double * >(&fAbsValue); + int nExponent = pValParts->inf_parts.exponent - 1023; + if (nExponent >= 52) + return 0; // All bits in fraction are in integer part of the number + int nLeastSignificant = findFirstSetBit(pValParts->inf_parts.fraction_lo); + if (nLeastSignificant == 0) + { + nLeastSignificant = findFirstSetBit(pValParts->inf_parts.fraction_hi); + if (nLeastSignificant == 0) + nLeastSignificant = 53; // the implied leading 1 is the least significant + else + nLeastSignificant += 32; + } + int nFracSignificant = 53 - nLeastSignificant; + int nBitsInFracPart = nFracSignificant - nExponent; + + return nBitsInFracPart > 0 ? nBitsInFracPart : 0; +} + template< typename T > inline void doubleToString(typename T::String ** pResult, sal_Int32 * pResultCapacity, sal_Int32 nResultOffset, @@ -1136,7 +1181,8 @@ double SAL_CALL rtl_math_pow10Exp(double fValue, int nExp) SAL_THROW_EXTERN_C() double SAL_CALL rtl_math_approxValue( double fValue ) SAL_THROW_EXTERN_C() { - if (fValue == 0.0 || fValue == HUGE_VAL || !::rtl::math::isFinite( fValue)) + const double fBigInt = 2199023255552.0; // 2^41 -> only 11 bits left for fractional part, fine as decimal + if (fValue == 0.0 || fValue == HUGE_VAL || !::rtl::math::isFinite( fValue) || fValue > fBigInt) { // We don't handle these conditions. Bail out. return fValue; @@ -1148,6 +1194,11 @@ double SAL_CALL rtl_math_approxValue( double fValue ) SAL_THROW_EXTERN_C() if (bSign) fValue = -fValue; + // If the value is either integer representable as double, + // or only has small number of bits in fraction part, then we need not do any approximation + if (isRepresentableInteger(fValue) || getBitsInFracPart(fValue) <= 11) + return fOrigValue; + int nExp = static_cast< int >(floor(log10(fValue))); nExp = 14 - nExp; double fExpValue = getN10Exp(nExp); |