New plugin: FFT, A frequency analyzer plugin

There is some more work needed:
- Keymaps are definitely not perfect, touchscreen targets are disabled due to no keymap
- There is no manual yet

Author: Delyan Kratunov 
Flyspray: FS#10065



git-svn-id: svn://svn.rockbox.org/rockbox/trunk@24587 a1c6a512-1295-4272-9138-f99709370657

apps/plugins/fft/math.h

@@ -0,0 +1,28 @@
+#ifndef __MATH_H_
+#define __MATH_H_
+
+#include <inttypes.h>
+#include <math.h>
+#include "lib/fixedpoint.h"
+
+#define Q_MUL(a, b, bits) (( (int64_t) (a) * (int64_t) (b) ) >> (bits))
+#define Q15_MUL(a, b) Q_MUL(a,b,15)
+#define Q16_MUL(a, b) Q_MUL(a,b,16)
+
+#define Q_DIV(a, b, bits) ( (((int64_t) (a)) << (bits)) / (b) )
+#define Q15_DIV(a, b) Q_DIV(a,b,15)
+#define Q16_DIV(a, b) Q_DIV(a,b,16)
+
+#define float_q(a, bits) (int32_t)( ((float)(a)) *(1<<(bits)))
+#define float_q15(a) float_q(a, 15)
+#define float_q16(a) float_q(a, 16)
+
+/**
+ * Fixed point square root via Newton-Raphson.
+ * @param a square root argument.
+ * @param fracbits specifies number of fractional bits in argument.
+ * @return Square root of argument in same fixed point format as input.
+ */
+int64_t fsqrt64(int64_t a, unsigned int fracbits);
+
+#endif