Merge pull request #142 from mb64/wrapping-sqrt

Change `sqrt` to use wrapping newtypes

Author: alexcrichton

src/math/sqrt.rs

@@ -77,6 +77,7 @@
  */
 
 use core::f64;
+use core::num::Wrapping;
 
 const TINY: f64 = 1.0e-300;
 
@@ -96,29 +97,29 @@ pub fn sqrt(x: f64) -> f64 {
         }
     }
     let mut z: f64;
-    let sign: u32 = 0x80000000;
+    let sign: Wrapping<u32> = Wrapping(0x80000000);
     let mut ix0: i32;
     let mut s0: i32;
     let mut q: i32;
     let mut m: i32;
     let mut t: i32;
     let mut i: i32;
-    let mut r: u32;
-    let mut t1: u32;
-    let mut s1: u32;
-    let mut ix1: u32;
-    let mut q1: u32;
+    let mut r: Wrapping<u32>;
+    let mut t1: Wrapping<u32>;
+    let mut s1: Wrapping<u32>;
+    let mut ix1: Wrapping<u32>;
+    let mut q1: Wrapping<u32>;
 
     ix0 = (x.to_bits() >> 32) as i32;
-    ix1 = x.to_bits() as u32;
+    ix1 = Wrapping(x.to_bits() as u32);
 
     /* take care of Inf and NaN */
     if (ix0 & 0x7ff00000) == 0x7ff00000 {
         return x * x + x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf, sqrt(-inf)=sNaN */
     }
     /* take care of zero */
     if ix0 <= 0 {
-        if ((ix0 & !(sign as i32)) | ix1 as i32) == 0 {
+        if ((ix0 & !(sign.0 as i32)) | ix1.0 as i32) == 0 {
             return x; /* sqrt(+-0) = +-0 */
         }
         if ix0 < 0 {
@@ -131,7 +132,7 @@ pub fn sqrt(x: f64) -> f64 {
         /* subnormal x */
         while ix0 == 0 {
             m -= 21;
-            ix0 |= (ix1 >> 11) as i32;
+            ix0 |= (ix1 >> 11).0 as i32;
             ix1 <<= 21;
         }
         i = 0;
@@ -140,46 +141,46 @@ pub fn sqrt(x: f64) -> f64 {
             ix0 <<= 1;
         }
         m -= i - 1;
-        ix0 |= (ix1 >> (32 - i)) as i32;
-        ix1 <<= i;
+        ix0 |= (ix1 >> (32 - i) as usize).0 as i32;
+        ix1 = ix1 << i as usize;
     }
     m -= 1023; /* unbias exponent */
     ix0 = (ix0 & 0x000fffff) | 0x00100000;
     if (m & 1) == 1 {
         /* odd m, double x to make it even */
-        ix0 += ix0 + ((ix1 & sign) >> 31) as i32;
+        ix0 += ix0 + ((ix1 & sign) >> 31).0 as i32;
         ix1 += ix1;
     }
     m >>= 1; /* m = [m/2] */
 
     /* generate sqrt(x) bit by bit */
-    ix0 += ix0 + ((ix1 & sign) >> 31) as i32;
+    ix0 += ix0 + ((ix1 & sign) >> 31).0 as i32;
     ix1 += ix1;
     q = 0; /* [q,q1] = sqrt(x) */
-    q1 = 0;
+    q1 = Wrapping(0);
     s0 = 0;
-    s1 = 0;
-    r = 0x00200000; /* r = moving bit from right to left */
+    s1 = Wrapping(0);
+    r = Wrapping(0x00200000); /* r = moving bit from right to left */
 
-    while r != 0 {
-        t = s0 + r as i32;
+    while r != Wrapping(0) {
+        t = s0 + r.0 as i32;
         if t <= ix0 {
-            s0 = t + r as i32;
+            s0 = t + r.0 as i32;
             ix0 -= t;
-            q += r as i32;
+            q += r.0 as i32;
         }
-        ix0 += ix0 + ((ix1 & sign) >> 31) as i32;
+        ix0 += ix0 + ((ix1 & sign) >> 31).0 as i32;
         ix1 += ix1;
         r >>= 1;
     }
 
     r = sign;
-    while r != 0 {
+    while r != Wrapping(0) {
         t1 = s1 + r;
         t = s0;
         if t < ix0 || (t == ix0 && t1 <= ix1) {
             s1 = t1 + r;
-            if (t1 & sign) == sign && (s1 & sign) == 0 {
+            if (t1 & sign) == sign && (s1 & sign) == Wrapping(0) {
                 s0 += 1;
             }
             ix0 -= t;
@@ -189,26 +190,26 @@ pub fn sqrt(x: f64) -> f64 {
             ix1 -= t1;
             q1 += r;
         }
-        ix0 += ix0 + ((ix1 & sign) >> 31) as i32;
+        ix0 += ix0 + ((ix1 & sign) >> 31).0 as i32;
         ix1 += ix1;
         r >>= 1;
     }
 
     /* use floating add to find out rounding direction */
-    if (ix0 as u32 | ix1) != 0 {
+    if (ix0 as u32 | ix1.0) != 0 {
         z = 1.0 - TINY; /* raise inexact flag */
         if z >= 1.0 {
             z = 1.0 + TINY;
-            if q1 == 0xffffffff {
-                q1 = 0;
+            if q1.0 == 0xffffffff {
+                q1 = Wrapping(0);
                 q += 1;
             } else if z > 1.0 {
-                if q1 == 0xfffffffe {
+                if q1.0 == 0xfffffffe {
                     q += 1;
                 }
-                q1 += 2;
+                q1 += Wrapping(2);
             } else {
-                q1 += q1 & 1;
+                q1 += q1 & Wrapping(1);
             }
         }
     }
@@ -218,5 +219,5 @@ pub fn sqrt(x: f64) -> f64 {
         ix1 |= sign;
     }
     ix0 += m << 20;
-    f64::from_bits((ix0 as u64) << 32 | ix1 as u64)
+    f64::from_bits((ix0 as u64) << 32 | ix1.0 as u64)
 }