loghelper(): Try to nudge the compiler into doing mults in an order that

tim-one · tim-one · commit e5ca6c71cd4a · 2001-09-05T04:33:11.000Z
minimizes roundoff error.
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
@@ -263,7 +263,7 @@ loghelper(PyObject* args, double (*func)(double), char *name)
 		   log(x) + log(2) * e * SHIFT.
 		   CAUTION:  e*SHIFT may overflow using int arithmetic,
 		   so force use of double. */
-		x = func(x) + func(2.0) * (double)e * (double)SHIFT;
+		x = func(x) + (e * (double)SHIFT) * func(2.0);
 		return PyFloat_FromDouble(x);
 	}
 

Original file line number	Diff line number	Diff line change
`@@ -263,7 +263,7 @@ loghelper(PyObject* args, double (func)(double), char name)`
`263`	`263`	`log(x) + log(2) * e * SHIFT.`
`264`	`264`	`CAUTION: e*SHIFT may overflow using int arithmetic,`
`265`	`265`	`so force use of double. */`
`266`		`- x = func(x) + func(2.0) * (double)e * (double)SHIFT;`
	`266`	`+ x = func(x) + (e * (double)SHIFT) * func(2.0);`
`267`	`267`	`return PyFloat_FromDouble(x);`
`268`	`268`	`}`
`269`	`269`