diff options
Diffstat (limited to 'sysdeps/ieee754/ldbl-128ibm/s_rintl.c')
| -rw-r--r-- | sysdeps/ieee754/ldbl-128ibm/s_rintl.c | 144 |
1 files changed, 72 insertions, 72 deletions
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_rintl.c b/sysdeps/ieee754/ldbl-128ibm/s_rintl.c index 51b1fea2c4..1f4e33f91c 100644 --- a/sysdeps/ieee754/ldbl-128ibm/s_rintl.c +++ b/sysdeps/ieee754/ldbl-128ibm/s_rintl.c @@ -22,6 +22,7 @@ when it's coded in C. */ #include <math.h> +#include <fenv_libc.h> #include <math_ldbl_opt.h> #include <float.h> #include <ieee754.h> @@ -36,84 +37,83 @@ __rintl (x) long double x; #endif { - static const long double TWO52 = 4503599627370496.0L; - union ibm_extended_long_double u; - u.d = x; + double xh, xl, hi, lo; - if (fabs (u.dd[0]) < TWO52) - { - double high = u.dd[0]; - if (high > 0.0) - { - high += TWO52; - high -= TWO52; - if (high == -0.0) high = 0.0; - } - else if (high < 0.0) - { - high -= TWO52; - high += TWO52; - if (high == 0.0) high = -0.0; - } - u.dd[0] = high; - u.dd[1] = 0.0; - } - else if (fabs (u.dd[1]) < TWO52 && u.dd[1] != 0.0) + ldbl_unpack (x, &xh, &xl); + + /* Return Inf, Nan, +/-0 unchanged. */ + if (__builtin_expect (xh != 0.0 + && __builtin_isless (__builtin_fabs (xh), + __builtin_inf ()), 1)) { - double high, low, tau; - /* In this case we have to round the low double and handle any - adjustment to the high double that may be caused by rounding - (up). This is complicated by the fact that the high double - may already be rounded and the low double may have the - opposite sign to compensate. */ - if (u.dd[0] > 0.0) - { - if (u.dd[1] > 0.0) - { - /* If the high/low doubles are the same sign then simply - round the low double. */ - high = u.dd[0]; - low = u.dd[1]; - } - else if (u.dd[1] < 0.0) - { - /* Else the high double is pre rounded and we need to - adjust for that. */ - - tau = nextafter (u.dd[0], 0.0); - tau = (u.dd[0] - tau) * 2.0; - high = u.dd[0] - tau; - low = u.dd[1] + tau; - } - low += TWO52; - low -= TWO52; - } - else if (u.dd[0] < 0.0) + double orig_xh; + int save_round = fegetround (); + + /* Long double arithmetic, including the canonicalisation below, + only works in round-to-nearest mode. */ + fesetround (FE_TONEAREST); + + /* Convert the high double to integer. */ + orig_xh = xh; + hi = ldbl_nearbyint (xh); + + /* Subtract integral high part from the value. If the low double + happens to be exactly 0.5 or -0.5, you might think that this + subtraction could result in an incorrect conversion. For + instance, subtracting an odd number would cause this function + to round in the wrong direction. However, if we have a + canonical long double with the low double 0.5 or -0.5, then the + high double must be even. */ + xh -= hi; + ldbl_canonicalize (&xh, &xl); + + /* Now convert the low double, adjusted for any remainder from the + high double. */ + lo = ldbl_nearbyint (xh); + + xh -= lo; + ldbl_canonicalize (&xh, &xl); + + switch (save_round) { - if (u.dd[1] < 0.0) - { - /* If the high/low doubles are the same sign then simply - round the low double. */ - high = u.dd[0]; - low = u.dd[1]; - } - else if (u.dd[1] > 0.0) - { - /* Else the high double is pre rounded and we need to - adjust for that. */ - tau = nextafter (u.dd[0], 0.0); - tau = (u.dd[0] - tau) * 2.0; - high = u.dd[0] - tau; - low = u.dd[1] + tau; - } - low = TWO52 - low; - low = -(low - TWO52); + case FE_TONEAREST: + if (xl > 0.0 && xh == 0.5) + lo += 1.0; + else if (xl < 0.0 && -xh == 0.5) + lo -= 1.0; + break; + + case FE_TOWARDZERO: + if (orig_xh < 0.0) + goto do_up; + /* Fall thru */ + + case FE_DOWNWARD: + if (xh < 0.0 || (xh == 0.0 && xl < 0.0)) + lo -= 1.0; + break; + + case FE_UPWARD: + do_up: + if (xh > 0.0 || (xh == 0.0 && xl > 0.0)) + lo += 1.0; + break; } - u.dd[0] = high + low; - u.dd[1] = high - u.dd[0] + low; + + /* Ensure the final value is canonical. In certain cases, + rounding causes hi,lo calculated so far to be non-canonical. */ + xh = hi; + xl = lo; + ldbl_canonicalize (&xh, &xl); + + /* Ensure we return -0 rather than +0 when appropriate. */ + if (orig_xh < 0.0) + xh = -__builtin_fabs (xh); + + fesetround (save_round); } - return u.d; + return ldbl_pack (xh, xl); } long_double_symbol (libm, __rintl, rintl); |