+
+# Expands to code that defines a function signbitf(float).
+# It extracts the sign bit of a non-NaN value.
+AC_DEFUN([gl_FLOAT_SIGNBIT_CODE],
+[
+ gl_FLOATTYPE_SIGNBIT_CODE([float], [f], [f])
+])
+
+# Expands to code that defines a function signbitd(double).
+# It extracts the sign bit of a non-NaN value.
+AC_DEFUN([gl_DOUBLE_SIGNBIT_CODE],
+[
+ gl_FLOATTYPE_SIGNBIT_CODE([double], [d], [])
+])
+
+# Expands to code that defines a function signbitl(long double).
+# It extracts the sign bit of a non-NaN value.
+AC_DEFUN([gl_LONG_DOUBLE_SIGNBIT_CODE],
+[
+ gl_FLOATTYPE_SIGNBIT_CODE([long double], [l], [L])
+])
+
+AC_DEFUN([gl_FLOATTYPE_SIGNBIT_CODE],
+[[
+static int
+signbit$2 ($1 value)
+{
+ typedef union { $1 f; unsigned char b[sizeof ($1)]; } float_union;
+ static float_union plus_one = { 1.0$3 }; /* unused bits are zero here */
+ static float_union minus_one = { -1.0$3 }; /* unused bits are zero here */
+ /* Compute the sign bit mask as the XOR of plus_one and minus_one. */
+ float_union u;
+ unsigned int i;
+ u.f = value;
+ for (i = 0; i < sizeof ($1); i++)
+ if (u.b[i] & (plus_one.b[i] ^ minus_one.b[i]))
+ return 1;
+ return 0;
+}
+]])