66 lines
1.7 KiB
C
66 lines
1.7 KiB
C
#include "libc/limits.h"
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#include "libc/math/fenv.h"
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#include "libc/math/libm.h"
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#include "libc/math/math.h"
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/*
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If the result cannot be represented (overflow, nan), then
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lrint raises the invalid exception.
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Otherwise if the input was not an integer then the inexact
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exception is raised.
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C99 is a bit vague about whether inexact exception is
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allowed to be raised when invalid is raised.
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(F.9 explicitly allows spurious inexact exceptions, F.9.6.5
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does not make it clear if that rule applies to lrint, but
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IEEE 754r 7.8 seems to forbid spurious inexact exception in
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the ineger conversion functions)
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So we try to make sure that no spurious inexact exception is
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raised in case of an overflow.
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If the bit size of long > precision of double, then there
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cannot be inexact rounding in case the result overflows,
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otherwise LONG_MAX and LONG_MIN can be represented exactly
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as a double.
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*/
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#if LONG_MAX < 1U << 53 && defined(FE_INEXACT)
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#if FLT_EVAL_METHOD == 0 || FLT_EVAL_METHOD == 1
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#define EPS DBL_EPSILON
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#elif FLT_EVAL_METHOD == 2
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#define EPS LDBL_EPSILON
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#endif
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#ifdef __GNUC__
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/* avoid stack frame in lrint */
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__attribute__((noinline))
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#endif
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static long
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lrint_slow(double x) {
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#pragma STDC FENV_ACCESS ON
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int e;
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e = fetestexcept(FE_INEXACT);
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x = rint(x);
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if (!e && (x > LONG_MAX || x < LONG_MIN)) feclearexcept(FE_INEXACT);
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/* conversion */
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return x;
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}
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long lrint(double x) {
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uint32_t abstop = asuint64(x) >> 32 & 0x7fffffff;
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uint64_t sign = asuint64(x) & (1ULL << 63);
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if (abstop < 0x41dfffff) {
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/* |x| < 0x7ffffc00, no overflow */
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double_t toint = asdouble(asuint64(1 / EPS) | sign);
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double_t y = x + toint - toint;
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return (long)y;
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}
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return lrint_slow(x);
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}
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#else
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long lrint(double x) { return rint(x); }
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#endif
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