C: mem. for audio: optimize; use the same function

Memory allocation for the audio buffer:
1. Instant mode: Use `malloc` instead of `calloc`
2. Allocate heap memory before the loop to speed up audio generation, free
   the memory after the loop
3. Extract the memory allocation into a macro

src/template.c

@@ -52,6 +52,17 @@ const char* ANSI_CLEAR = __ANSI_CLEAR_STRING;
 #define unsigned_to_signed(x) (x - PCM_COEFFICIENT)
 #define signed_to_unsigned(x) (x + PCM_COEFFICIENT)
 
+// macros
+#define ALLOCATE_MEMORY(nmemb)                                                \
+    SAMPLE_TYPE* buffer = malloc(                                             \
+        (size_t) nmemb * sizeof(SAMPLE_TYPE)                                  \
+    );                                                                        \
+                                                                              \
+    if (buffer == NULL) {                                                     \
+        perror("malloc");                                                     \
+        return EXIT_FAILURE;                                                  \
+    }
+
 // global variables
 #define SILENT_MODE `silent_mode`
 #define VERBOSE_MODE `verbose_mode`
@@ -198,28 +209,24 @@ main(void)
 	}
 
 	const size_t MAX = (PRODUCT + (BLOCK_SIZE - 1)) / BLOCK_SIZE;
+#endif
 
+    // * allocate heap for sample data
+#if SEQUENTIAL_MODE
+	size_t calc_block_size = BLOCK_SIZE;
+	ALLOCATE_MEMORY(calc_block_size)
+#else
+	ALLOCATE_MEMORY(PRODUCT)
+#endif
+
+#if SEQUENTIAL_MODE
 	size_t w = 0;
 	for (size_t seq = 0; seq < MAX; seq++) {
-		size_t calc_block_size = BLOCK_SIZE;
 		if ((w + BLOCK_SIZE) >= PRODUCT)
 			calc_block_size = PRODUCT - w;
 #else
 	do {
 #endif
-		// * allocate heap for sample data
-		SAMPLE_TYPE* buffer =
-#if SEQUENTIAL_MODE
-			malloc((size_t) calc_block_size *
-#else
-			calloc(PRODUCT,
-#endif
-			sizeof(SAMPLE_TYPE));
-
-		if (buffer == NULL) {
-			perror("calloc");
-			return 1;
-		}
 
 		// * bytebeat generating loop
 		const uintmax_t product_minus_1 = PRODUCT - 1,
@@ -324,14 +331,14 @@ main(void)
 #if SEQUENTIAL_MODE
 		fflush(output_file);
 #endif
-
-		// * free allocated heap
-		free(buffer);
 	}
 #if !SEQUENTIAL_MODE
 		while (0);
 #endif
 
+	// * free allocated heap
+	free(buffer);
+
 	// 6. close file
 	fclose(output_file);