C: add fwrite_le.*

c-programming/fwrite_le.c

@@ -0,0 +1,91 @@
+#include "fwrite_le.h"
+
+int detect_endianness(void) {
+	volatile uint32_t i = 0x01234567;
+	uint8_t* bytes = (uint8_t*)(&i);
+	if (bytes[0] == 0x01 &&
+		bytes[1] == 0x23 &&
+		bytes[2] == 0x45 &&
+		bytes[3] == 0x67)
+		return DETECTED_BIG_ENDIAN;
+	else if (
+		bytes[0] == 0x67 &&
+		bytes[1] == 0x45 &&
+		bytes[2] == 0x23 &&
+		bytes[3] == 0x01)
+		return DETECTED_LITTLE_ENDIAN;
+	return UNSUPPORTED_ENDIANNESS;
+}
+
+void reorder_le_be(
+#if FWRITE_LE_NO_MODIFICATION
+	uint8_t* dest, uint8_t* src,
+#else
+	uint8_t* bytes,
+#endif
+	size_t count, size_t step) {
+	for (size_t i = 0; i < count; i += step) {
+		const size_t div_size = step / 2;
+		for (size_t j = 0; j < div_size; j++) {
+			const size_t old_pos = i + j, new_pos = i + step - j - 1;
+#if FWRITE_LE_NO_MODIFICATION
+			dest[old_pos] = src[new_pos];
+			dest[new_pos] = src[old_pos];
+#else
+			uint8_t temp = bytes[old_pos];
+			bytes[old_pos] = bytes[new_pos];
+			bytes[new_pos] = temp;
+#endif
+		}
+	}
+}
+
+size_t fwrite_le(void* ptr, size_t size, size_t count, FILE* stream) {
+	/*
+	 * warning: this function modifies `void* ptr` by default!
+	 *          (if FWRITE_LE_NO_MODIFICATION in the header is 0)
+	 */
+	if (ptr == NULL)
+		return 0;
+
+	int endianness = detect_endianness();
+	if (endianness == UNSUPPORTED_ENDIANNESS) {
+		fprintf(stderr, "Unsupported endianness\n");
+		exit(EXIT_FAILURE);
+	} else if (endianness == DETECTED_LITTLE_ENDIAN)
+		return fwrite(ptr, size, count, stream);
+
+	// case: big-endian
+	size_t bytes_count = size * count;
+#if FWRITE_LE_NO_MODIFICATION
+	uint8_t* bytes = calloc(bytes_count, sizeof(uint8_t));
+	if (bytes == NULL) {
+		perror("calloc");
+		exit(EXIT_FAILURE);
+	}
+	memcpy(bytes, ptr, bytes_count);
+#endif
+
+	reorder_le_be(
+#if FWRITE_LE_NO_MODIFICATION
+		bytes,
+#endif
+		(uint8_t*) ptr, bytes_count, size);
+
+#if FWRITE_LE_NO_MODIFICATION
+	size_t res =
+#else
+	return
+#endif
+		fwrite(
+#if FWRITE_LE_NO_MODIFICATION
+			bytes,
+#else
+			(uint8_t*) ptr,
+#endif
+			size, count, stream);
+#if FWRITE_LE_NO_MODIFICATION
+	free(bytes);
+	return res;
+#endif
+}

c-programming/fwrite_le.h

@@ -0,0 +1,25 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifndef _FWRITE_LE_H
+#define _FWRITE_LE_H
+
+#define FWRITE_LE_NO_MODIFICATION 0
+
+#define DETECTED_LITTLE_ENDIAN 0
+#define DETECTED_BIG_ENDIAN 1
+#define UNSUPPORTED_ENDIANNESS -1
+
+int detect_endianness(void);
+size_t fwrite_le(void* ptr, size_t size, size_t count, FILE* stream);
+void reorder_le_be(
+#if FWRITE_LE_NO_MODIFICATION
+	uint8_t* dest, uint8_t* src,
+#else
+	uint8_t* bytes,
+#endif
+	size_t count, size_t step);
+
+#endif /* _FWRITE_LE_H */