Math: Complex: Calculate complex phase angle with sofm_atan2()

This patch updates the phase angle calculation in function
sofm_icomple32_to_polar() with more efficient sofm_atan2()
function. Calculate of angle with arctan function avoids the
64 bit divide in the previous arccos function based calculation.

In 48 kHz stereo STFT processing with 1024 size FFT and hop of
256 this change saves about 14 MCPS in MTL platform (204 MCPS
to 190 MCPS).

Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>

Author: singalsu

src/math/Kconfig

@@ -108,6 +108,9 @@ config MATH_DECIBELS
 config MATH_COMPLEX
 	bool "Operations for complex numbers"
 	default n
+	select CORDIC_FIXED
+	select MATH_ATAN2
+	select SQRT_FIXED
 	help
 	  Select this to enable functions for complex numbers
 	  arithmetic such as conversions to/from polar format.

src/math/complex.c

@@ -9,6 +9,7 @@
 #include <sof/audio/format.h>
 #include <sof/math/icomplex32.h>
 #include <sof/math/sqrt.h>
+#include <sof/math/trig.h>
 #include <stdint.h>
 
 /* sofm_icomplex32_to_polar() - Convert (re, im) complex number to polar. */
@@ -17,8 +18,6 @@ void sofm_icomplex32_to_polar(struct icomplex32 *complex, struct ipolar32 *polar
 	struct icomplex32 c = *complex;
 	int64_t squares_sum;
 	int32_t sqrt_arg;
-	int32_t acos_arg;
-	int32_t acos_val;
 
 	/* Calculate square of magnitudes Q1.31, result is Q2.62 */
 	squares_sum = (int64_t)c.real * c.real + (int64_t)c.imag * c.imag;
@@ -27,16 +26,8 @@ void sofm_icomplex32_to_polar(struct icomplex32 *complex, struct ipolar32 *polar
 	sqrt_arg = Q_SHIFT_RND(squares_sum, 62, 30);
 	polar->magnitude = sofm_sqrt_int32(sqrt_arg); /* Q2.30 */
 
-	/* Avoid divide by zero and ambiguous angle for a zero vector. */
-	if (polar->magnitude == 0) {
-		polar->angle = 0;
-		return;
-	}
-
-	/* Calculate phase angle with acos( complex->real / polar->magnitude) */
-	acos_arg = sat_int32((((int64_t)c.real) << 29) / polar->magnitude); /* Q2.30 */
-	acos_val = acos_fixed_32b(acos_arg);				    /* Q3.29 */
-	polar->angle = (c.imag < 0) ? -acos_val : acos_val;
+	/* Angle */
+	polar->angle = sofm_atan2_32b(c.imag, c.real); /* Q3.29 */
 }
 EXPORT_SYMBOL(sofm_icomplex32_to_polar);
 

test/ztest/unit/math/basic/complex/CMakeLists.txt

@@ -22,6 +22,7 @@ target_sources(app PRIVATE
 	${SOF_ROOT}/src/math/complex.c
 	${SOF_ROOT}/src/math/sqrt_int32.c
 	${SOF_ROOT}/src/math/trig.c
+	${SOF_ROOT}/src/math/atan2.c
 )
 
 # Link math library for standard math functions