Add newlib sqrtf

Author: tesuji

src/math/sqrtf.rs

@@ -0,0 +1,115 @@
+/* ef_sqrtf.c -- float version of e_sqrt.c.
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, [email protected].
+ */
+
+/*
+ * ====================================================
+ * 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.
+ * ====================================================
+ */
+
+const ONE: f32 = 1.0;
+const TINY: f32 = 1.0e-30;
+
+#[inline]
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn sqrtf(x: f32) -> f32 {
+    use super::fdlibm::{FLT_UWORD_IS_FINITE, FLT_UWORD_IS_SUBNORMAL, FLT_UWORD_IS_ZERO};
+    // On wasm32 we know that LLVM's intrinsic will compile to an optimized
+    // `f32.sqrt` native instruction, so we can leverage this for both code size
+    // and speed.
+    llvm_intrinsically_optimized! {
+        #[cfg(target_arch = "wasm32")] {
+            return if x < 0.0 {
+                ::core::f32::NAN
+            } else {
+                unsafe { ::core::intrinsics::sqrtf32(x) }
+            }
+        }
+    }
+
+    let mut z: f32;
+
+    let mut r: u32;
+    let hx: u32;
+
+    let mut ix: i32;
+    let mut s: i32;
+    let mut q: i32;
+    let mut m: i32;
+    let mut t: i32;
+    let mut i: i32;
+
+    ix = x.to_bits() as i32;
+    hx = ix as u32 & 0x7fff_ffff;
+
+    /* take care of Inf and NaN */
+    if !FLT_UWORD_IS_FINITE(hx) {
+        return x * x + x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf, sqrt(-inf)=sNaN */
+    }
+
+    /* take care of zero and -ves */
+    if FLT_UWORD_IS_ZERO(hx) {
+        return x; /* sqrt(+-0) = +-0 */
+    }
+    if ix < 0 {
+        return (x - x) / (x - x); /* sqrt(-ve) = sNaN */
+    }
+
+    /* normalize x */
+    m = ix >> 23;
+    if FLT_UWORD_IS_SUBNORMAL(hx) {
+        /* subnormal x */
+        i = 0;
+        while ix & 0x0080_0000 == 0 {
+            ix <<= 1;
+            i += 1;
+        }
+        m -= i - 1;
+    }
+    m -= 127; /* unbias exponent */
+    ix = (ix & 0x007f_ffff) | 0x0080_0000;
+    /* odd m, double x to make it even */
+    if m & 1 == 1 {
+        ix += ix;
+    }
+    m >>= 1; /* m = [m/2] */
+
+    /* generate sqrt(x) bit by bit */
+    ix += ix;
+    q = 0;
+    s = 0; /* q = sqrt(x) */
+    r = 0x0100_0000; /* r = moving bit from right to left */
+
+    while r != 0 {
+        t = s + r as i32;
+        if t <= ix {
+            s = t + r as i32;
+            ix -= t;
+            q += r as i32;
+        }
+        ix += ix;
+        r >>= 1;
+    }
+
+    /* use floating add to find out rounding direction */
+    if ix != 0 {
+        z = ONE - TINY; /* trigger inexact flag */
+        if z >= ONE {
+            z = ONE + TINY;
+            if z > ONE {
+                q += 2;
+            } else {
+                q += q & 1;
+            }
+        }
+    }
+    ix = (q >> 1) + 0x3f00_0000;
+    ix += m << 23;
+    f32::from_bits(ix as u32)
+}