From ff5608e0d0ff070f1723e7a6f96ac26fe8957825 Mon Sep 17 00:00:00 2001
From: Intel A80486DX2-66 <larry.holst@disroot.org>
Date: Sun, 31 Dec 2023 15:19:42 +0300
Subject: [PATCH] C: add fwrite_le.*, correct include var. in template

---
 src/fwrite_le.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/fwrite_le.h | 18 +++++++++++++
 src/template.c  |  2 +-
 3 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 src/fwrite_le.c
 create mode 100644 src/fwrite_le.h

diff --git a/src/fwrite_le.c b/src/fwrite_le.c
new file mode 100644
index 0000000..5ab9a1a
--- /dev/null
+++ b/src/fwrite_le.c
@@ -0,0 +1,68 @@
+#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;
+}
+
+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);
+#else
+	uint8_t* bytes = (uint8_t*) ptr;
+#endif
+
+	for (size_t i = 0; i < bytes_count; i += size) {
+		const size_t div_size = size >> 1; // divide by 2
+		for (size_t j = 0; j < div_size; j++) {
+			const size_t old_pos = i + j, new_pos = i + size - j - 1;
+			uint8_t temp = bytes[old_pos];
+			bytes[old_pos] = bytes[new_pos];
+			bytes[new_pos] = temp;
+		}
+	}
+
+#if FWRITE_LE_NO_MODIFICATION
+	size_t res =
+#else
+	return
+#endif
+		fwrite(bytes, size, count, stream);
+#if FWRITE_LE_NO_MODIFICATION
+	free(bytes);
+	return res;
+#endif
+}
diff --git a/src/fwrite_le.h b/src/fwrite_le.h
new file mode 100644
index 0000000..aa61722
--- /dev/null
+++ b/src/fwrite_le.h
@@ -0,0 +1,18 @@
+#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);
+
+#endif /* _FWRITE_LE_H */
diff --git a/src/template.c b/src/template.c
index b3e1ea6..aa66b1c 100644
--- a/src/template.c
+++ b/src/template.c
@@ -7,7 +7,7 @@
 #include <string.h>
 #include <time.h>
 
-#include "`path_to_fwrite_le`"
+#include "`fwrite_le`"
 
 // constants
 #if defined(_WIN32)