From: Taylor R Campbell <campbell@mumble.net>
Date: Sun, 18 Nov 2018 23:06:46 +0000 (+0000)
Subject: Avoid overflow in sqrt(1 - z^2) with sqrt(1 - z)*sqrt(1 + z) in asin.
X-Git-Tag: mit-scheme-pucked-10.1.2~16^2~18
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=210f3c37d3af418bd9fddf6f2d85335a6ceaa9b8;p=mit-scheme.git

Avoid overflow in sqrt(1 - z^2) with sqrt(1 - z)*sqrt(1 + z) in asin.

Strike off a couple xfails.  Others remain because the branch cuts
are busted.
---

diff --git a/src/runtime/arith.scm b/src/runtime/arith.scm
index 4c143134c..54b2322f1 100644
--- a/src/runtime/arith.scm
+++ b/src/runtime/arith.scm
@@ -1796,7 +1796,9 @@ USA.
 	   (complex:-i*
 	    (complex:log
 	     (complex:+ (complex:+i* z)
-			(complex:sqrt (complex:- 1 (complex:* z z)))))))))
+			(complex:*
+			 (complex:sqrt (complex:+ 1 z))
+			 (complex:sqrt (complex:- 1 z)))))))))
     (let ((unsafe-case
 	   (lambda (z)
 	     (complex:negate (safe-case (complex:negate z))))))
diff --git a/tests/runtime/test-arith.scm b/tests/runtime/test-arith.scm
index 966d67236..391726d76 100644
--- a/tests/runtime/test-arith.scm
+++ b/tests/runtime/test-arith.scm
@@ -513,9 +513,9 @@ USA.
    (vector -1e150-0.i -1.5707963267948966-346.0809111296668i 'xfail)
    (vector 1e300 1.5707963267948966+691.4686750787736i 'xfail)
    (vector 1e300+0.i 1.5707963267948966+691.4686750787736i 'xfail)
-   (vector 1e300-0.i 1.5707963267948966-691.4686750787736i 'xfail)
-   (vector -1e300 -1.5707963267948966+691.4686750787736i 'xfail)
-   (vector -1e300+0.i -1.5707963267948966+691.4686750787736i 'xfail)
+   (vector 1e300-0.i 1.5707963267948966-691.4686750787736i)
+   (vector -1e300 -1.5707963267948966+691.4686750787736i)
+   (vector -1e300+0.i -1.5707963267948966+691.4686750787736i)
    (vector -1e300-0.i -1.5707963267948966-691.4686750787736i 'xfail))
   (lambda (v)
     (let ((x (vector-ref v 0))