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authorupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
committerupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
commit554fd8c5195424bdbcabf5de30fdc183aba391bd (patch)
tree976dc5ab7fddf506dadce60ae936f43f58787092 /libquadmath/math/cbrtq.c
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Diffstat (limited to 'libquadmath/math/cbrtq.c')
-rw-r--r--libquadmath/math/cbrtq.c64
1 files changed, 64 insertions, 0 deletions
diff --git a/libquadmath/math/cbrtq.c b/libquadmath/math/cbrtq.c
new file mode 100644
index 000000000..f61f32513
--- /dev/null
+++ b/libquadmath/math/cbrtq.c
@@ -0,0 +1,64 @@
+#include "quadmath-imp.h"
+#include <math.h>
+#include <float.h>
+
+__float128
+cbrtq (const __float128 x)
+{
+ __float128 y;
+ int exp, i;
+
+ if (x == 0)
+ return x;
+
+ if (isnanq (x))
+ return x;
+
+ if (x <= DBL_MAX && x >= DBL_MIN)
+ {
+ /* Use double result as starting point. */
+ y = cbrt ((double) x);
+
+ /* Two Newton iterations. */
+ y -= 0.333333333333333333333333333333333333333333333333333Q
+ * (y - x / (y * y));
+ y -= 0.333333333333333333333333333333333333333333333333333Q
+ * (y - x / (y * y));
+ return y;
+ }
+
+#ifdef HAVE_CBRTL
+ if (x <= LDBL_MAX && x >= LDBL_MIN)
+ {
+ /* Use long double result as starting point. */
+ y = cbrtl ((long double) x);
+
+ /* One Newton iteration. */
+ y -= 0.333333333333333333333333333333333333333333333333333Q
+ * (y - x / (y * y));
+ return y;
+ }
+#endif
+
+ /* If we're outside of the range of C types, we have to compute
+ the initial guess the hard way. */
+ y = frexpq (x, &exp);
+
+ i = exp % 3;
+ y = (i >= 0 ? i : -i);
+ if (i == 1)
+ y *= 2, exp--;
+ else if (i == 2)
+ y *= 4, exp -= 2;
+
+ y = cbrt (y);
+ y = scalbnq (y, exp / 3);
+
+ /* Two Newton iterations. */
+ y -= 0.333333333333333333333333333333333333333333333333333Q
+ * (y - x / (y * y));
+ y -= 0.333333333333333333333333333333333333333333333333333Q
+ * (y - x / (y * y));
+ return y;
+}
+