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Clear errno before using errcheck() to avoid spurious errors. (#80)

The errcheck() function treats an errno of ERANGE or EDOM as something
to report, so make sure errno is set to zero before invoking a
function to check so that a previous such errno value won't result
in a false positive.  This could happen simply due to input line fields
that looked enough like floating-point input to trigger ERANGE.

Reported by Jordan Geoghegan, fix from Philip Guenther.

--- a/run.c

+++ b/run.c

@@ -25,6 +25,7 @@

 #define DEBUG

 #include <stdio.h>

 #include <ctype.h>

+#include <errno.h>

 #include <wchar.h>

 #include <wctype.h>

 #include <fcntl.h>

@@ -1072,8 +1073,10 @@

 	case POWER:

 		if (j >= 0 && modf(j, &v) == 0.0)	/* pos integer exponent */

 			i = ipow(i, (int) j);

-		else

+               else {

+			errno = 0;

 			i = errcheck(pow(i, j), "pow");

+               }

 		break;

 	default:	/* can't happen */

 		FATAL("illegal arithmetic operator %d", n);

@@ -1166,8 +1169,10 @@

 	case POWEQ:

 		if (yf >= 0 && modf(yf, &v) == 0.0)	/* pos integer exponent */

 			xf = ipow(xf, (int) yf);

-		else

+               else {

+			errno = 0;

 			xf = errcheck(pow(xf, yf), "pow");

+               }

 		break;

 	default:

 		FATAL("illegal assignment operator %d", n);

@@ -1589,13 +1594,19 @@

 			u = strlen(getsval(x));

 		break;

 	case FLOG:

-		u = errcheck(log(getfval(x)), "log"); break;

+		errno = 0;

+		u = errcheck(log(getfval(x)), "log");

+		break;

 	case FINT:

 		modf(getfval(x), &u); break;

 	case FEXP:

-		u = errcheck(exp(getfval(x)), "exp"); break;

+		errno = 0;

+		u = errcheck(exp(getfval(x)), "exp");

+		break;

 	case FSQRT:

-		u = errcheck(sqrt(getfval(x)), "sqrt"); break;

+		errno = 0;

+		u = errcheck(sqrt(getfval(x)), "sqrt");

+		break;

 	case FSIN:

 		u = sin(getfval(x)); break;

 	case FCOS:

-- 

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