diff options
Diffstat (limited to '')
| -rw-r--r-- | vendor/compiler_builtins/libm/src/math/log10.rs | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/vendor/compiler_builtins/libm/src/math/log10.rs b/vendor/compiler_builtins/libm/src/math/log10.rs new file mode 100644 index 000000000..40dacf2c9 --- /dev/null +++ b/vendor/compiler_builtins/libm/src/math/log10.rs @@ -0,0 +1,117 @@ +/* origin: FreeBSD /usr/src/lib/msun/src/e_log10.c */ +/* + * ==================================================== + * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. + * + * Developed at SunSoft, a Sun Microsystems, Inc. business. + * Permission to use, copy, modify, and distribute this + * software is freely granted, provided that this notice + * is preserved. + * ==================================================== + */ +/* + * Return the base 10 logarithm of x. See log.c for most comments. + * + * Reduce x to 2^k (1+f) and calculate r = log(1+f) - f + f*f/2 + * as in log.c, then combine and scale in extra precision: + * log10(x) = (f - f*f/2 + r)/log(10) + k*log10(2) + */ + +use core::f64; + +const IVLN10HI: f64 = 4.34294481878168880939e-01; /* 0x3fdbcb7b, 0x15200000 */ +const IVLN10LO: f64 = 2.50829467116452752298e-11; /* 0x3dbb9438, 0xca9aadd5 */ +const LOG10_2HI: f64 = 3.01029995663611771306e-01; /* 0x3FD34413, 0x509F6000 */ +const LOG10_2LO: f64 = 3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */ +const LG1: f64 = 6.666666666666735130e-01; /* 3FE55555 55555593 */ +const LG2: f64 = 3.999999999940941908e-01; /* 3FD99999 9997FA04 */ +const LG3: f64 = 2.857142874366239149e-01; /* 3FD24924 94229359 */ +const LG4: f64 = 2.222219843214978396e-01; /* 3FCC71C5 1D8E78AF */ +const LG5: f64 = 1.818357216161805012e-01; /* 3FC74664 96CB03DE */ +const LG6: f64 = 1.531383769920937332e-01; /* 3FC39A09 D078C69F */ +const LG7: f64 = 1.479819860511658591e-01; /* 3FC2F112 DF3E5244 */ + +#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] +pub fn log10(mut x: f64) -> f64 { + let x1p54 = f64::from_bits(0x4350000000000000); // 0x1p54 === 2 ^ 54 + + let mut ui: u64 = x.to_bits(); + let hfsq: f64; + let f: f64; + let s: f64; + let z: f64; + let r: f64; + let mut w: f64; + let t1: f64; + let t2: f64; + let dk: f64; + let y: f64; + let mut hi: f64; + let lo: f64; + let mut val_hi: f64; + let mut val_lo: f64; + let mut hx: u32; + let mut k: i32; + + hx = (ui >> 32) as u32; + k = 0; + if hx < 0x00100000 || (hx >> 31) > 0 { + if ui << 1 == 0 { + return -1. / (x * x); /* log(+-0)=-inf */ + } + if (hx >> 31) > 0 { + return (x - x) / 0.0; /* log(-#) = NaN */ + } + /* subnormal number, scale x up */ + k -= 54; + x *= x1p54; + ui = x.to_bits(); + hx = (ui >> 32) as u32; + } else if hx >= 0x7ff00000 { + return x; + } else if hx == 0x3ff00000 && ui << 32 == 0 { + return 0.; + } + + /* reduce x into [sqrt(2)/2, sqrt(2)] */ + hx += 0x3ff00000 - 0x3fe6a09e; + k += (hx >> 20) as i32 - 0x3ff; + hx = (hx & 0x000fffff) + 0x3fe6a09e; + ui = (hx as u64) << 32 | (ui & 0xffffffff); + x = f64::from_bits(ui); + + f = x - 1.0; + hfsq = 0.5 * f * f; + s = f / (2.0 + f); + z = s * s; + w = z * z; + t1 = w * (LG2 + w * (LG4 + w * LG6)); + t2 = z * (LG1 + w * (LG3 + w * (LG5 + w * LG7))); + r = t2 + t1; + + /* See log2.c for details. */ + /* hi+lo = f - hfsq + s*(hfsq+R) ~ log(1+f) */ + hi = f - hfsq; + ui = hi.to_bits(); + ui &= (-1i64 as u64) << 32; + hi = f64::from_bits(ui); + lo = f - hi - hfsq + s * (hfsq + r); + + /* val_hi+val_lo ~ log10(1+f) + k*log10(2) */ + val_hi = hi * IVLN10HI; + dk = k as f64; + y = dk * LOG10_2HI; + val_lo = dk * LOG10_2LO + (lo + hi) * IVLN10LO + lo * IVLN10HI; + + /* + * Extra precision in for adding y is not strictly needed + * since there is no very large cancellation near x = sqrt(2) or + * x = 1/sqrt(2), but we do it anyway since it costs little on CPUs + * with some parallelism and it reduces the error for many args. + */ + w = y + val_hi; + val_lo += (y - w) + val_hi; + val_hi = w; + + val_lo + val_hi +} |