fix infinite recursion in divmoddi4 / mulodi4

Jorge Aparicio · Jorge Aparicio · commit 644a1c9ac972 · 2017-03-06T10:38:19.000-05:00
on ARMv7-M processors, divmoddi4 was calling mulodi4 and mulodi4 was calling divmoddi4 leading to infinite recursion. This commit breaks the cycle by using wrapping multiplication in divmoddi4. fixes rust-lang#145
diff --git a/src/int/sdiv.rs b/src/int/sdiv.rs
@@ -55,7 +55,9 @@ macro_rules! divmod {
                 #[cfg(all(feature = "c", any(target_arch = "x86")))]
                 () => unsafe { $div(a, b) },
             };
-            *rem = a - (r * b);
+            // NOTE won't overflow because it's using the result from the
+            // previous division
+            *rem = a - r.wrapping_mul(b);
             r
         }
     }

Original file line number	Diff line number	Diff line change
`@@ -55,7 +55,9 @@ macro_rules! divmod {`
`55`	`55`	`#[cfg(all(feature = "c", any(target_arch = "x86")))]`
`56`	`56`	`() => unsafe { $div(a, b) },`
`57`	`57`	`};`
`58`		`- rem = a - (r b);`
	`58`	`+ // NOTE won't overflow because it's using the result from the`
	`59`	`+ // previous division`
	`60`	`+ *rem = a - r.wrapping_mul(b);`
`59`	`61`	`r`
`60`	`62`	`}`
`61`	`63`	`}`