diff options
Diffstat (limited to 'hypot.c')
| -rw-r--r-- | hypot.c | 6 |
1 files changed, 4 insertions, 2 deletions
@@ -85,9 +85,11 @@ mpfr_hypot (mpfr_ptr z, mpfr_srcptr x , mpfr_srcptr y , mp_rnd_t rnd_mode) y does not overlap with the result when x^2+y^2 < (|x| + 1/2*ulp(x,Nz))^2 = x^2 + |x|*ulp(x,Nz) + 1/4*ulp(x,Nz)^2, i.e. a sufficient condition is y^2 < |x|*ulp(x,Nz), - or 2^(2*Ey) <= 2^(2*Ex-1-Nz), i.e. 2*diff_exp > Nz + or 2^(2*Ey) <= 2^(2*Ex-1-Nz), i.e. 2*diff_exp > Nz. + Warning: this is true only for Nx <= Nz, otherwise the trailing bits + of x may be already very close to 1/2*ulp(x,Nz)! */ - if (diff_exp > Nz / 2) /* result is |x| or |x|+ulp(|x|,Nz) */ + if (MPFR_PREC(x) <= Nz && diff_exp > Nz / 2) /* result is |x| or |x|+ulp(|x|,Nz) */ { if (rnd_mode == GMP_RNDU) { |