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+/* origin: FreeBSD /usr/src/lib/msun/src/e_log10f.c */
+/*
+ * ====================================================
+ * 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.
+ * ====================================================
+ */
+/*
+ * See comments in log10.c.
+ */
+
+use core::f32;
+
+const IVLN10HI: f32 = 4.3432617188e-01; /* 0x3ede6000 */
+const IVLN10LO: f32 = -3.1689971365e-05; /* 0xb804ead9 */
+const LOG10_2HI: f32 = 3.0102920532e-01; /* 0x3e9a2080 */
+const LOG10_2LO: f32 = 7.9034151668e-07; /* 0x355427db */
+/* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
+const LG1: f32 = 0.66666662693; /* 0xaaaaaa.0p-24 */
+const LG2: f32 = 0.40000972152; /* 0xccce13.0p-25 */
+const LG3: f32 = 0.28498786688; /* 0x91e9ee.0p-25 */
+const LG4: f32 = 0.24279078841; /* 0xf89e26.0p-26 */
+
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn log10f(mut x: f32) -> f32 {
+ let x1p25f = f32::from_bits(0x4c000000); // 0x1p25f === 2 ^ 25
+
+ let mut ui: u32 = x.to_bits();
+ let hfsq: f32;
+ let f: f32;
+ let s: f32;
+ let z: f32;
+ let r: f32;
+ let w: f32;
+ let t1: f32;
+ let t2: f32;
+ let dk: f32;
+ let mut hi: f32;
+ let lo: f32;
+ let mut ix: u32;
+ let mut k: i32;
+
+ ix = ui;
+ k = 0;
+ if ix < 0x00800000 || (ix >> 31) > 0 {
+ /* x < 2**-126 */
+ if ix << 1 == 0 {
+ return -1. / (x * x); /* log(+-0)=-inf */
+ }
+ if (ix >> 31) > 0 {
+ return (x - x) / 0.0; /* log(-#) = NaN */
+ }
+ /* subnormal number, scale up x */
+ k -= 25;
+ x *= x1p25f;
+ ui = x.to_bits();
+ ix = ui;
+ } else if ix >= 0x7f800000 {
+ return x;
+ } else if ix == 0x3f800000 {
+ return 0.;
+ }
+
+ /* reduce x into [sqrt(2)/2, sqrt(2)] */
+ ix += 0x3f800000 - 0x3f3504f3;
+ k += (ix >> 23) as i32 - 0x7f;
+ ix = (ix & 0x007fffff) + 0x3f3504f3;
+ ui = ix;
+ x = f32::from_bits(ui);
+
+ f = x - 1.0;
+ s = f / (2.0 + f);
+ z = s * s;
+ w = z * z;
+ t1 = w * (LG2 + w * LG4);
+ t2 = z * (LG1 + w * LG3);
+ r = t2 + t1;
+ hfsq = 0.5 * f * f;
+
+ hi = f - hfsq;
+ ui = hi.to_bits();
+ ui &= 0xfffff000;
+ hi = f32::from_bits(ui);
+ lo = f - hi - hfsq + s * (hfsq + r);
+ dk = k as f32;
+ dk * LOG10_2LO + (lo + hi) * IVLN10LO + lo * IVLN10HI + hi * IVLN10HI + dk * LOG10_2HI
+}