Math: Optimise 16-bit matrix multiplication functions.

Improve mat_multiply and mat_multiply_elementwise for 16-bit signed
integers by refactoring operations and simplifying handling of Q0 data.
Both functions now use incremented pointers in loop expressions for
better legibility and potential compiler optimisation.

Changes: - Improved x pointer increments in mat_multiply.
- Integrating Q0 conditional logic into the main flow.
- Clean up the mat_multiply_elementwise loop structure.
- Ensure precision with appropriate fractional bit shifts.

These modifications aim to improve accuracy and efficiency in
fixed-point arithmetic operations.

Signed-off-by: Shriram Shastry <malladi.sastry@intel.com>

src/math/matrix.c

@@ -3,6 +3,7 @@
 // Copyright(c) 2022 Intel Corporation. All rights reserved.
 //
 // Author: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>
+//         Shriram Shastry <malladi.sastry@linux.intel.com>
 
 #include <sof/math/matrix.h>
 #include <errno.h>
@@ -11,47 +12,24 @@
 int mat_multiply(struct mat_matrix_16b *a, struct mat_matrix_16b *b, struct mat_matrix_16b *c)
 {
 	int64_t s;
-	int16_t *x;
-	int16_t *y;
-	int16_t *z = c->data;
+	int16_t *x, *y, *z = c->data;
 	int i, j, k;
 	int y_inc = b->columns;
-	const int shift_minus_one = a->fractions + b->fractions - c->fractions - 1;
+	const int shift = a->fractions + b->fractions - c->fractions - 1;
 
 	if (a->columns != b->rows || a->rows != c->rows || b->columns != c->columns)
 		return -EINVAL;
 
-	/* If all data is Q0 */
-	if (shift_minus_one == -1) {
-		for (i = 0; i < a->rows; i++) {
-			for (j = 0; j < b->columns; j++) {
-				s = 0;
-				x = a->data + a->columns * i;
-				y = b->data + j;
-				for (k = 0; k < b->rows; k++) {
-					s += (int32_t)(*x) * (*y);
-					x++;
-					y += y_inc;
-				}
-				*z = (int16_t)s; /* For Q16.0 */
-				z++;
-			}
-		}
-
-		return 0;
-	}
-
 	for (i = 0; i < a->rows; i++) {
 		for (j = 0; j < b->columns; j++) {
-			s = 0;
-			x = a->data + a->columns * i;
-			y = b->data + j;
+			s = 0; x = a->data + a->columns * i; y = b->data + j;
 			for (k = 0; k < b->rows; k++) {
-				s += (int32_t)(*x) * (*y);
-				x++;
-				y += y_inc;
+				s += (int32_t)(*x++) * (*y); y += y_inc;
 			}
-			*z = (int16_t)(((s >> shift_minus_one) + 1) >> 1); /*Shift to Qx.y */
+			if (shift == -1)
+				*z = (int16_t)s;
+			else
+				*z = (int16_t)(((s >> shift) + 1) >> 1);
 			z++;
 		}
 	}
@@ -60,36 +38,30 @@ int mat_multiply(struct mat_matrix_16b *a, struct mat_matrix_16b *b, struct mat_
 
 int mat_multiply_elementwise(struct mat_matrix_16b *a, struct mat_matrix_16b *b,
 			     struct mat_matrix_16b *c)
-{	int64_t p;
+{
+	if (a->columns != b->columns || a->rows != b->rows)
+		return -EINVAL;
+
+	const int total_elements = a->rows * a->columns;
+	const int shift_minus_one = a->fractions + b->fractions - c->fractions - 1;
+
 	int16_t *x = a->data;
 	int16_t *y = b->data;
 	int16_t *z = c->data;
+	int64_t p;
 	int i;
-	const int shift_minus_one = a->fractions + b->fractions - c->fractions - 1;
-
-	if (a->columns != b->columns || b->columns != c->columns ||
-	    a->rows != b->rows || b->rows != c->rows) {
-		return -EINVAL;
-	}
 
-	/* If all data is Q0 */
 	if (shift_minus_one == -1) {
-		for (i = 0; i < a->rows * a->columns; i++) {
-			*z = *x * *y;
-			x++;
-			y++;
-			z++;
-		}
+		// If all data is Q0
+		for (i = 0; i < total_elements; i++)
+			z[i] = x[i] * y[i];
 
-		return 0;
-	}
-
-	for (i = 0; i < a->rows * a->columns; i++) {
-		p = (int32_t)(*x) * *y;
-		*z = (int16_t)(((p >> shift_minus_one) + 1) >> 1); /*Shift to Qx.y */
-		x++;
-		y++;
-		z++;
+	} else {
+		// General case
+		for (i = 0; i < total_elements; i++) {
+			p = (int32_t)x[i] * y[i];
+			z[i] = (int16_t)(((p >> shift_minus_one) + 1) >> 1); // Shift to Qx.y
+		}
 	}
 
 	return 0;