diff options
Diffstat (limited to 'sysdeps/ieee754/dbl-64/e_exp2.c')
| -rw-r--r-- | sysdeps/ieee754/dbl-64/e_exp2.c | 97 |
1 files changed, 48 insertions, 49 deletions
diff --git a/sysdeps/ieee754/dbl-64/e_exp2.c b/sysdeps/ieee754/dbl-64/e_exp2.c index 4cf879b7f9..e57ec92116 100644 --- a/sysdeps/ieee754/dbl-64/e_exp2.c +++ b/sysdeps/ieee754/dbl-64/e_exp2.c @@ -61,57 +61,56 @@ __ieee754_exp2 (double x) int tval, unsafe; double rx, x22, result; union ieee754_double ex2_u, scale_u; - fenv_t oldenv; - - libc_feholdexcept_setround (&oldenv, FE_TONEAREST); - - /* 1. Argument reduction. - Choose integers ex, -256 <= t < 256, and some real - -1/1024 <= x1 <= 1024 so that - x = ex + t/512 + x1. - - First, calculate rx = ex + t/512. */ - rx = x + THREEp42; - rx -= THREEp42; - x -= rx; /* Compute x=x1. */ - /* Compute tval = (ex*512 + t)+256. - Now, t = (tval mod 512)-256 and ex=tval/512 [that's mod, NOT %; and - /-round-to-nearest not the usual c integer /]. */ - tval = (int) (rx * 512.0 + 256.0); - - /* 2. Adjust for accurate table entry. - Find e so that - x = ex + t/512 + e + x2 - where -1e6 < e < 1e6, and - (double)(2^(t/512+e)) - is accurate to one part in 2^-64. */ - - /* 'tval & 511' is the same as 'tval%512' except that it's always - positive. - Compute x = x2. */ - x -= exp2_deltatable[tval & 511]; - - /* 3. Compute ex2 = 2^(t/512+e+ex). */ - ex2_u.d = exp2_accuratetable[tval & 511]; - tval >>= 9; - unsafe = abs(tval) >= -DBL_MIN_EXP - 1; - ex2_u.ieee.exponent += tval >> unsafe; - scale_u.d = 1.0; - scale_u.ieee.exponent += tval - (tval >> unsafe); - - /* 4. Approximate 2^x2 - 1, using a fourth-degree polynomial, - with maximum error in [-2^-10-2^-30,2^-10+2^-30] - less than 10^-19. */ - - x22 = (((.0096181293647031180 - * x + .055504110254308625) - * x + .240226506959100583) - * x + .69314718055994495) * ex2_u.d; - math_opt_barrier (x22); - /* 5. Return (2^x2-1) * 2^(t/512+e+ex) + 2^(t/512+e+ex). */ - libc_fesetenv (&oldenv); + { + SET_RESTORE_ROUND_NOEX (FE_TONEAREST); + + /* 1. Argument reduction. + Choose integers ex, -256 <= t < 256, and some real + -1/1024 <= x1 <= 1024 so that + x = ex + t/512 + x1. + + First, calculate rx = ex + t/512. */ + rx = x + THREEp42; + rx -= THREEp42; + x -= rx; /* Compute x=x1. */ + /* Compute tval = (ex*512 + t)+256. + Now, t = (tval mod 512)-256 and ex=tval/512 [that's mod, NOT %; + and /-round-to-nearest not the usual c integer /]. */ + tval = (int) (rx * 512.0 + 256.0); + + /* 2. Adjust for accurate table entry. + Find e so that + x = ex + t/512 + e + x2 + where -1e6 < e < 1e6, and + (double)(2^(t/512+e)) + is accurate to one part in 2^-64. */ + + /* 'tval & 511' is the same as 'tval%512' except that it's always + positive. + Compute x = x2. */ + x -= exp2_deltatable[tval & 511]; + + /* 3. Compute ex2 = 2^(t/512+e+ex). */ + ex2_u.d = exp2_accuratetable[tval & 511]; + tval >>= 9; + unsafe = abs(tval) >= -DBL_MIN_EXP - 1; + ex2_u.ieee.exponent += tval >> unsafe; + scale_u.d = 1.0; + scale_u.ieee.exponent += tval - (tval >> unsafe); + + /* 4. Approximate 2^x2 - 1, using a fourth-degree polynomial, + with maximum error in [-2^-10-2^-30,2^-10+2^-30] + less than 10^-19. */ + + x22 = (((.0096181293647031180 + * x + .055504110254308625) + * x + .240226506959100583) + * x + .69314718055994495) * ex2_u.d; + math_opt_barrier (x22); + } + /* 5. Return (2^x2-1) * 2^(t/512+e+ex) + 2^(t/512+e+ex). */ result = x22 * x + ex2_u.d; if (!unsafe) |