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-rw-r--r--libquadmath/math/sqrtq.c57
1 files changed, 57 insertions, 0 deletions
diff --git a/libquadmath/math/sqrtq.c b/libquadmath/math/sqrtq.c
new file mode 100644
index 000000000..6ed4605ed
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+++ b/libquadmath/math/sqrtq.c
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+#include "quadmath-imp.h"
+#include <math.h>
+#include <float.h>
+
+__float128
+sqrtq (const __float128 x)
+{
+ __float128 y;
+ int exp;
+
+ if (x == 0)
+ return x;
+
+ if (isnanq (x))
+ return x;
+
+ if (x < 0)
+ return nanq ("");
+
+ if (x <= DBL_MAX && x >= DBL_MIN)
+ {
+ /* Use double result as starting point. */
+ y = sqrt ((double) x);
+
+ /* Two Newton iterations. */
+ y -= 0.5q * (y - x / y);
+ y -= 0.5q * (y - x / y);
+ return y;
+ }
+
+#ifdef HAVE_SQRTL
+ if (x <= LDBL_MAX && x >= LDBL_MIN)
+ {
+ /* Use long double result as starting point. */
+ y = sqrtl ((long double) x);
+
+ /* One Newton iteration. */
+ y -= 0.5q * (y - x / 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);
+ if (exp % 2)
+ y *= 2, exp--;
+
+ y = sqrt (y);
+ y = scalbnq (y, exp / 2);
+
+ /* Two Newton iterations. */
+ y -= 0.5q * (y - x / y);
+ y -= 0.5q * (y - x / y);
+ return y;
+}
+