changed from Hart & Cheney to Cody & Waite

lang/cem/libcc.ansi/math/asin.c

@@ -6,31 +6,61 @@
  */
 /* $Header$ */
 
-#include	<errno.h>
 #include	<math.h>
+#include	<errno.h>
 #include	"localmath.h"
 
-
 static double
 asin_acos(double x, int cosfl)
 {
 	int negative = x < 0;
+	int     i;
+	double  g;
+	static double p[] = {
+		-0.27368494524164255994e+2,
+		 0.57208227877891731407e+2,
+		-0.39688862997540877339e+2,
+		 0.10152522233806463645e+2,
+		-0.69674573447350646411e+0
+	};
+	static double q[] = {
+		-0.16421096714498560795e+3,
+		 0.41714430248260412556e+3,
+		-0.38186303361750149284e+3,
+		 0.15095270841030604719e+3,
+		-0.23823859153670238830e+2,
+		 1.0
+	};
 
 	if (negative) {
 		x = -x;
 	}
-	if (x > 1) {
-		errno = EDOM;
-		return 0;
+	if (x > 0.5) {
+		i = 1;
+		if (x > 1) {
+			errno = EDOM;
+			return 0;
+		}
+		g = 0.5 - 0.5 * x;
+		x = - sqrt(g);
+		x += x;
 	}
-	if (x == 1) {
-		x = M_PI_2;
+	else {
+		/* ??? avoid underflow ??? */
+		i = 0;
+		g = x * x;
 	}
-	else x = atan(x/sqrt(1-x*x));
-	if (negative) x = -x;
+	x += x * g * POLYNOM4(g, p) / POLYNOM5(g, q);
 	if (cosfl) {
-		return M_PI_2 - x;
+		if (! negative) x = -x;
 	}
+	if ((cosfl == 0) == (i == 1)) {
+		x = (x + M_PI_4) + M_PI_4;
+	}
+	else if (cosfl && negative && i == 1) {
+		x = (x + M_PI_2) + M_PI_2;
+	}
+	if (! cosfl && negative) x = -x;
 	return x;
 }