allow force_eval! to produce a result and use that result to more explicitly force rounding on x87.

Author: Peter Michael Green

libm/src/math/fma.rs

@@ -220,7 +220,8 @@ mod tests {
 
         let result = fma(-0.992, -0.992, -0.992);
         //force rounding to storage format on x87 to prevent superious errors.
-        #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]force_eval!(result);
+        #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
+        let result = force_eval!(result);
         assert_eq!(result, -0.007936000000000007,);
     }
 

libm/src/math/mod.rs

@@ -1,7 +1,7 @@
 macro_rules! force_eval {
     ($e:expr) => {
         unsafe {
-            ::core::ptr::read_volatile(&$e);
+            ::core::ptr::read_volatile(&$e)
         }
     };
 }

libm/src/math/pow.rs

@@ -484,8 +484,10 @@ mod tests {
                 let exp = expected(*val);
                 let res = computed(*val);
 
-                #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]force_eval!(exp);
-                #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]force_eval!(res);
+                #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
+                let exp = force_eval!(exp);
+                #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
+                let res = force_eval!(res);
                 assert!(
                     if exp.is_nan() {
                         res.is_nan()

libm/src/math/rem_pio2.rs

@@ -53,7 +53,8 @@ pub(crate) fn rem_pio2(x: f64) -> (i32, f64, f64) {
         let tmp = x as f64 * INV_PIO2 + TO_INT;
         // force rounding of tmp to it's storage format on x87 to avoid
         // excess precision issues.
-        #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]force_eval!(tmp);
+        #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
+        let tmp = force_eval!(tmp);
         let f_n = tmp - TO_INT;
         let n = f_n as i32;
         let mut r = x - f_n * PIO2_1;
@@ -195,25 +196,25 @@ mod tests {
     #[test]
     fn test_near_pi() {
         let arg = 3.141592025756836;
-        force_eval!(arg);
+        let arg = force_eval!(arg);
         assert_eq!(
             rem_pio2(arg),
             (2, -6.278329573009626e-7, -2.1125998133974653e-23)
         );
         let arg = 3.141592033207416;
-        force_eval!(arg);
+        let arg = force_eval!(arg);
         assert_eq!(
             rem_pio2(arg),
             (2, -6.20382377148128e-7, -2.1125998133974653e-23)
         );
         let arg = 3.141592144966125;
-        force_eval!(arg);
+        let arg = force_eval!(arg);
         assert_eq!(
             rem_pio2(arg),
             (2, -5.086236681942706e-7, -2.1125998133974653e-23)
         );
         let arg = 3.141592979431152;
-        force_eval!(arg);
+        let arg = force_eval!(arg);
         assert_eq!(
             rem_pio2(arg),
             (2, 3.2584135866119817e-7, -2.1125998133974653e-23)

libm/src/math/rem_pio2f.rs

@@ -46,7 +46,8 @@ pub(crate) fn rem_pio2f(x: f32) -> (i32, f64) {
         let tmp = x64 * INV_PIO2 + TOINT;
         // force rounding of tmp to it's storage format on x87 to avoid
         // excess precision issues.
-        #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]force_eval!(tmp);
+        #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
+        let tmp = force_eval!(tmp);
         let f_n = tmp - TOINT;
         return (f_n as i32, x64 - f_n * PIO2_1 - f_n * PIO2_1T);
     }

libm/src/math/sin.rs

@@ -82,6 +82,7 @@ fn test_near_pi() {
     let x = f64::from_bits(0x400921fb000FD5DD); // 3.141592026217707
     let sx = f64::from_bits(0x3ea50d15ced1a4a2); // 6.273720864039205e-7
     let result = sin(x);
-    #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]force_eval!(result);
+    #[cfg(all(target_arch = "x86", not(target_feature = "sse2")))]
+    let result = force_eval!(result);
     assert_eq!(result, sx);
 }