From 06696f40afe58a231e2531c8bf6d9f0dadb92e51 Mon Sep 17 00:00:00 2001
From: Jakob Kaivo <jkk@ung.org>
Date: Sun, 3 Mar 2019 21:25:50 -0500
Subject: outline details from C18 annex F

---
 src/math/pow.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)

(limited to 'src/math/pow.c')

diff --git a/src/math/pow.c b/src/math/pow.c
index c0d613e5..8a070005 100644
--- a/src/math/pow.c
+++ b/src/math/pow.c
@@ -2,10 +2,91 @@
 #include <math.h>
 #include "_tgmath.h"
 #include "errno.h"
+#include "fenv.h"
 
 /** exponentiation **/
 TYPE TGFN(pow)(TYPE x, TYPE y)
 {
+	int classx = fpclassify(x);
+	int classy = fpclassify(y);
+
+	if (classx == FP_ZERO) {
+		if (classy == FP_INFINITE && signbit(y)) {
+			feraiseexcept(FE_DIVBYZERO);
+			return INFINITY;
+		}
+
+		if (y < 0) {
+			feraiseexcept(FE_DIVBYZERO);
+			/* if (y == odd integer) { */
+				return signbit(x) ? - INFINITY : INFINITY;
+			/* } else { */
+				return INFINITY;
+			/* } */
+		}
+
+		if (y > 0) {
+			/* if (y == odd integer) { */
+				return x;
+			/* } else { */
+				return 0.0;
+			/* } */
+		}
+	}
+
+	if (x == -1.0 && classy == FP_INFINITE) {
+		return 1;
+	}
+
+	if (x == 1.0) {
+		return 1.0;
+	}
+
+	if (classy == FP_ZERO) {
+		return 1.0;
+	}
+
+	if (x < 0 /* && y != integer */) {
+		feraiseexcept(FE_INVALID);
+		return NAN;
+	}
+
+	if (classy == FP_INFINITE) {
+		int sb = signbit(y);
+		TYPE ab = TGFN(fabs)(x);
+		if ((sb && ab < 1.0) || (!sb && ab > 1.0)) {
+			return INFINITY;
+		} else {
+			return 0.0;
+		}
+	}
+
+	if (classx == FP_INFINITE) {
+		if (!signbit(x)) {
+			if (y < 0) {
+				return 0.0;
+			} else if (y > 0) {
+				return INFINITY;
+			}
+		}
+
+		if (y < 0) {
+			/* if (y == odd integer ) { */
+				return -0.0;
+			/* } else { */
+				return 0.0;
+			/* } */
+		}
+
+		if (y > 0) {
+			/* if (y == odd integer ) { */
+				return - INFINITY;
+			/* } else { */
+				return INFINITY;
+			/* } */
+		}
+	}
+
 	if (x < 0 /* && !isintegral(y) */) {
 		errno = EDOM; /* ARGUMENT(x) is negative and ARGUMENT(y) is not an integer */
 		return TGHUGE;
-- 
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