lib/libm: Add frexp and modf functions; use in stmhal; add tests.

Addresses issue #1081.

1 files changed, 82 insertions, 0 deletions

diff --git a/lib/libm/sf_modf.c b/lib/libm/sf_modf.c
new file mode 100644
index 0000000000..4fcae057a5
--- /dev/null
+++ b/lib/libm/sf_modf.c
@@ -0,0 +1,82 @@
+/*
+ * This file is part of the Micro Python project, http://micropython.org/
+ *
+ * These math functions are taken from newlib-nano-2, the newlib/libm/common
+ * directory, available from https://github.com/32bitmicro/newlib-nano-2.
+ *
+ * Appropriate copyright headers are reproduced below.
+ */
+
+/* sf_modf.c -- float version of s_modf.c.
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ */
+
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice 
+ * is preserved.
+ * ====================================================
+ */
+
+#include "fdlibm.h"
+
+#ifdef __STDC__
+static const float one = 1.0;
+#else
+static float one = 1.0;
+#endif
+
+#ifdef __STDC__
+	float modff(float x, float *iptr)
+#else
+	float modff(x, iptr)
+	float x,*iptr;
+#endif
+{
+	__int32_t i0,j0;
+	__uint32_t i;
+	GET_FLOAT_WORD(i0,x);
+	j0 = ((i0>>23)&0xff)-0x7f;	/* exponent of x */
+	if(j0<23) {			/* integer part in x */
+	    if(j0<0) {			/* |x|<1 */
+	        SET_FLOAT_WORD(*iptr,i0&0x80000000);	/* *iptr = +-0 */
+		return x;
+	    } else {
+		i = (0x007fffff)>>j0;
+		if((i0&i)==0) {			/* x is integral */
+		    __uint32_t ix;
+		    *iptr = x;
+		    GET_FLOAT_WORD(ix,x);
+		    SET_FLOAT_WORD(x,ix&0x80000000);	/* return +-0 */
+		    return x;
+		} else {
+		    SET_FLOAT_WORD(*iptr,i0&(~i));
+		    return x - *iptr;
+		}
+	    }
+	} else {			/* no fraction part */
+	    __uint32_t ix;
+	    *iptr = x*one;
+	    GET_FLOAT_WORD(ix,x);
+	    SET_FLOAT_WORD(x,ix&0x80000000);	/* return +-0 */
+	    return x;
+	}
+}
+
+#ifdef _DOUBLE_IS_32BITS
+
+#ifdef __STDC__
+	double modf(double x, double *iptr)
+#else
+	double modf(x, iptr)
+	double x,*iptr;
+#endif
+{
+	return (double) modff((float) x, (float *) iptr);
+}
+
+#endif /* defined(_DOUBLE_IS_32BITS) */