diff --git a/src/math/exp2f.rs b/src/math/exp2f.rs
index 12c9e76a4..c777dc654 100644
--- a/src/math/exp2f.rs
+++ b/src/math/exp2f.rs
@@ -1,136 +1,33 @@
-// origin: FreeBSD /usr/src/lib/msun/src/s_exp2f.c
-//-
-// Copyright (c) 2005 David Schultz <das@FreeBSD.ORG>
-// All rights reserved.
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions
-// are met:
-// 1. Redistributions of source code must retain the above copyright
-// notice, this list of conditions and the following disclaimer.
-// 2. Redistributions in binary form must reproduce the above copyright
-// notice, this list of conditions and the following disclaimer in the
-// documentation and/or other materials provided with the distribution.
-//
-// THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
-// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-// ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
-// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
-// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
-// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
-// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
-// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
-// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
-// SUCH DAMAGE.
-
-const TBLSIZE: usize = 16;
-
-static EXP2FT: [u64; TBLSIZE] = [
- 0x3fe6a09e667f3bcd,
- 0x3fe7a11473eb0187,
- 0x3fe8ace5422aa0db,
- 0x3fe9c49182a3f090,
- 0x3feae89f995ad3ad,
- 0x3fec199bdd85529c,
- 0x3fed5818dcfba487,
- 0x3feea4afa2a490da,
- 0x3ff0000000000000,
- 0x3ff0b5586cf9890f,
- 0x3ff172b83c7d517b,
- 0x3ff2387a6e756238,
- 0x3ff306fe0a31b715,
- 0x3ff3dea64c123422,
- 0x3ff4bfdad5362a27,
- 0x3ff5ab07dd485429,
-];
-
-// exp2f(x): compute the base 2 exponential of x
-//
-// Accuracy: Peak error < 0.501 ulp; location of peak: -0.030110927.
-//
-// Method: (equally-spaced tables)
-//
-// Reduce x:
-// x = k + y, for integer k and |y| <= 1/2.
-// Thus we have exp2f(x) = 2**k * exp2(y).
-//
-// Reduce y:
-// y = i/TBLSIZE + z for integer i near y * TBLSIZE.
-// Thus we have exp2(y) = exp2(i/TBLSIZE) * exp2(z),
-// with |z| <= 2**-(TBLSIZE+1).
-//
-// We compute exp2(i/TBLSIZE) via table lookup and exp2(z) via a
-// degree-4 minimax polynomial with maximum error under 1.4 * 2**-33.
-// Using double precision for everything except the reduction makes
-// roundoff error insignificant and simplifies the scaling step.
-//
-// This method is due to Tang, but I do not use his suggested parameters:
-//
-// Tang, P. Table-driven Implementation of the Exponential Function
-// in IEEE Floating-Point Arithmetic. TOMS 15(2), 144-157 (1989).
+/* wf_exp2.c -- float version of w_exp2.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::powf;
/// Exponential, base 2 (f32)
///
/// Calculate `2^x`, that is, 2 raised to the power `x`.
#[inline]
#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
-pub fn exp2f(mut x: f32) -> f32 {
- let redux = f32::from_bits(0x4b400000) / TBLSIZE as f32;
- let p1 = f32::from_bits(0x3f317218);
- let p2 = f32::from_bits(0x3e75fdf0);
- let p3 = f32::from_bits(0x3d6359a4);
- let p4 = f32::from_bits(0x3c1d964e);
-
- // double_t t, r, z;
- // uint32_t ix, i0, k;
-
- let x1p127 = f32::from_bits(0x7f000000);
+pub fn exp2f(x: f32) -> f32 {
+ powf(2f32, x)
+}
- /* Filter out exceptional cases. */
- let ui = f32::to_bits(x);
- let ix = ui & 0x7fffffff;
- if ix > 0x42fc0000 {
- /* |x| > 126 */
- if ix > 0x7f800000 {
- /* NaN */
- return x;
- }
- if ui >= 0x43000000 && ui < 0x80000000 {
- /* x >= 128 */
- x *= x1p127;
- return x;
- }
- if ui >= 0x80000000 {
- /* x < -126 */
- if ui >= 0xc3160000 || (ui & 0x0000ffff != 0) {
- force_eval!(f32::from_bits(0x80000001) / x);
- }
- if ui >= 0xc3160000 {
- /* x <= -150 */
- return 0.0;
- }
- }
- } else if ix <= 0x33000000 {
- /* |x| <= 0x1p-25 */
- return 1.0 + x;
+#[cfg(test)]
+mod tests {
+ #[test]
+ fn sanity_check() {
+ assert_eq!(super::exp2f(1.1), 2.143547);
}
-
- /* Reduce x, computing z, i0, and k. */
- let ui = f32::to_bits(x + redux);
- let mut i0 = ui;
- i0 += TBLSIZE as u32 / 2;
- let k = i0 / TBLSIZE as u32;
- let ukf = f64::from_bits(((0x3ff + k) as u64) << 52);
- i0 &= TBLSIZE as u32 - 1;
- let mut uf = f32::from_bits(ui);
- uf -= redux;
- let z: f64 = (x - uf) as f64;
- /* Compute r = exp2(y) = exp2ft[i0] * p(z). */
- let r: f64 = f64::from_bits(EXP2FT[i0 as usize]);
- let t: f64 = r as f64 * z;
- let r: f64 = r + t * (p1 as f64 + z * p2 as f64) + t * (z * z) * (p3 as f64 + z * p4 as f64);
-
- /* Scale by 2**k */
- (r * ukf) as f32
}