diff options
Diffstat (limited to 'library/compiler-builtins/libm/src/math/jnf.rs')
| -rw-r--r-- | library/compiler-builtins/libm/src/math/jnf.rs | 253 |
1 files changed, 253 insertions, 0 deletions
diff --git a/library/compiler-builtins/libm/src/math/jnf.rs b/library/compiler-builtins/libm/src/math/jnf.rs new file mode 100644 index 00000000000..52cf7d8a8bd --- /dev/null +++ b/library/compiler-builtins/libm/src/math/jnf.rs @@ -0,0 +1,253 @@ +/* origin: FreeBSD /usr/src/lib/msun/src/e_jnf.c */ +/* + * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. + */ +/* + * ==================================================== + * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. + * + * Developed at SunPro, a Sun Microsystems, Inc. business. + * Permission to use, copy, modify, and distribute this + * software is freely granted, provided that this notice + * is preserved. + * ==================================================== + */ + +use super::{fabsf, j0f, j1f, logf, y0f, y1f}; + +/// Integer order of the [Bessel function](https://en.wikipedia.org/wiki/Bessel_function) of the first kind (f32). +#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] +pub fn jnf(n: i32, mut x: f32) -> f32 { + let mut ix: u32; + let mut nm1: i32; + let mut sign: bool; + let mut i: i32; + let mut a: f32; + let mut b: f32; + let mut temp: f32; + + ix = x.to_bits(); + sign = (ix >> 31) != 0; + ix &= 0x7fffffff; + if ix > 0x7f800000 { + /* nan */ + return x; + } + + /* J(-n,x) = J(n,-x), use |n|-1 to avoid overflow in -n */ + if n == 0 { + return j0f(x); + } + if n < 0 { + nm1 = -(n + 1); + x = -x; + sign = !sign; + } else { + nm1 = n - 1; + } + if nm1 == 0 { + return j1f(x); + } + + sign &= (n & 1) != 0; /* even n: 0, odd n: signbit(x) */ + x = fabsf(x); + if ix == 0 || ix == 0x7f800000 { + /* if x is 0 or inf */ + b = 0.0; + } else if (nm1 as f32) < x { + /* Safe to use J(n+1,x)=2n/x *J(n,x)-J(n-1,x) */ + a = j0f(x); + b = j1f(x); + i = 0; + while i < nm1 { + i += 1; + temp = b; + b = b * (2.0 * (i as f32) / x) - a; + a = temp; + } + } else if ix < 0x35800000 { + /* x < 2**-20 */ + /* x is tiny, return the first Taylor expansion of J(n,x) + * J(n,x) = 1/n!*(x/2)^n - ... + */ + if nm1 > 8 { + /* underflow */ + nm1 = 8; + } + temp = 0.5 * x; + b = temp; + a = 1.0; + i = 2; + while i <= nm1 + 1 { + a *= i as f32; /* a = n! */ + b *= temp; /* b = (x/2)^n */ + i += 1; + } + b = b / a; + } else { + /* use backward recurrence */ + /* x x^2 x^2 + * J(n,x)/J(n-1,x) = ---- ------ ------ ..... + * 2n - 2(n+1) - 2(n+2) + * + * 1 1 1 + * (for large x) = ---- ------ ------ ..... + * 2n 2(n+1) 2(n+2) + * -- - ------ - ------ - + * x x x + * + * Let w = 2n/x and h=2/x, then the above quotient + * is equal to the continued fraction: + * 1 + * = ----------------------- + * 1 + * w - ----------------- + * 1 + * w+h - --------- + * w+2h - ... + * + * To determine how many terms needed, let + * Q(0) = w, Q(1) = w(w+h) - 1, + * Q(k) = (w+k*h)*Q(k-1) - Q(k-2), + * When Q(k) > 1e4 good for single + * When Q(k) > 1e9 good for double + * When Q(k) > 1e17 good for quadruple + */ + /* determine k */ + let mut t: f32; + let mut q0: f32; + let mut q1: f32; + let mut w: f32; + let h: f32; + let mut z: f32; + let mut tmp: f32; + let nf: f32; + let mut k: i32; + + nf = (nm1 as f32) + 1.0; + w = 2.0 * nf / x; + h = 2.0 / x; + z = w + h; + q0 = w; + q1 = w * z - 1.0; + k = 1; + while q1 < 1.0e4 { + k += 1; + z += h; + tmp = z * q1 - q0; + q0 = q1; + q1 = tmp; + } + t = 0.0; + i = k; + while i >= 0 { + t = 1.0 / (2.0 * ((i as f32) + nf) / x - t); + i -= 1; + } + a = t; + b = 1.0; + /* estimate log((2/x)^n*n!) = n*log(2/x)+n*ln(n) + * Hence, if n*(log(2n/x)) > ... + * single 8.8722839355e+01 + * double 7.09782712893383973096e+02 + * long double 1.1356523406294143949491931077970765006170e+04 + * then recurrent value may overflow and the result is + * likely underflow to zero + */ + tmp = nf * logf(fabsf(w)); + if tmp < 88.721679688 { + i = nm1; + while i > 0 { + temp = b; + b = 2.0 * (i as f32) * b / x - a; + a = temp; + i -= 1; + } + } else { + i = nm1; + while i > 0 { + temp = b; + b = 2.0 * (i as f32) * b / x - a; + a = temp; + /* scale b to avoid spurious overflow */ + let x1p60 = f32::from_bits(0x5d800000); // 0x1p60 == 2^60 + if b > x1p60 { + a /= b; + t /= b; + b = 1.0; + } + i -= 1; + } + } + z = j0f(x); + w = j1f(x); + if fabsf(z) >= fabsf(w) { + b = t * z / b; + } else { + b = t * w / a; + } + } + + if sign { -b } else { b } +} + +/// Integer order of the [Bessel function](https://en.wikipedia.org/wiki/Bessel_function) of the second kind (f32). +#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] +pub fn ynf(n: i32, x: f32) -> f32 { + let mut ix: u32; + let mut ib: u32; + let nm1: i32; + let mut sign: bool; + let mut i: i32; + let mut a: f32; + let mut b: f32; + let mut temp: f32; + + ix = x.to_bits(); + sign = (ix >> 31) != 0; + ix &= 0x7fffffff; + if ix > 0x7f800000 { + /* nan */ + return x; + } + if sign && ix != 0 { + /* x < 0 */ + return 0.0 / 0.0; + } + if ix == 0x7f800000 { + return 0.0; + } + + if n == 0 { + return y0f(x); + } + if n < 0 { + nm1 = -(n + 1); + sign = (n & 1) != 0; + } else { + nm1 = n - 1; + sign = false; + } + if nm1 == 0 { + if sign { + return -y1f(x); + } else { + return y1f(x); + } + } + + a = y0f(x); + b = y1f(x); + /* quit if b is -inf */ + ib = b.to_bits(); + i = 0; + while i < nm1 && ib != 0xff800000 { + i += 1; + temp = b; + b = (2.0 * (i as f32) / x) * b - a; + ib = b.to_bits(); + a = temp; + } + + if sign { -b } else { b } +} |