From 02c4591d445dfe2cb29891b2c0d6a56722808d05 Mon Sep 17 00:00:00 2001
From: augustin64 <augustin.lucas64@gmail.com>
Date: Sat, 19 Mar 2022 16:54:16 +0100
Subject: [PATCH] Update src/preview_mnist.c

---
 src/preview_mnist.c | 50 ++++++++++++++++++++++++++++++++-------------
 1 file changed, 36 insertions(+), 14 deletions(-)

diff --git a/src/preview_mnist.c b/src/preview_mnist.c
index b1d1df5..9ddbed6 100644
--- a/src/preview_mnist.c
+++ b/src/preview_mnist.c
@@ -4,6 +4,12 @@
 #include <inttypes.h>
 
 
+uint32_t swap_endian(uint32_t val) {
+    val = ((val << 8) & 0xFF00FF00) | ((val >> 8) & 0xFF00FF);
+    return (val << 16) | (val >> 16);
+}
+
+
 void print_image(unsigned int width, unsigned int height, FILE* ptr, int start) {
     unsigned char buffer[width*height+start];
 
@@ -19,37 +25,53 @@ void print_image(unsigned int width, unsigned int height, FILE* ptr, int start)
         }
         printf("\n");
     }
-    printf("\t\t---\n");
 }
 
 
-
-void print_bytes(char* filename) {
+void read_mnist_images(char* filename) {
     unsigned char buffer[4];
     FILE *ptr;
     
     ptr = fopen(filename, "rb");
 
-    fread(buffer, sizeof(buffer), 1, ptr);
+    uint32_t magic_number;
+    uint32_t number_of_images;
+    unsigned int height;
+    unsigned int width;
 
-    uint32_t magic_number = buffer[0];
-    uint32_t number_of_images = (int)buffer[1];
-    unsigned int height = buffer[2];
-    unsigned int width = buffer[3];
+    fread(&magic_number, sizeof(uint32_t), 1, ptr);
+    magic_number = swap_endian(magic_number);
 
+    if (magic_number != 2051){
+        printf("Incorrect magic number !\n");
+        exit(1);
+    }
 
-    printf("magic number: %" PRIu32 "\n", magic_number);
-    printf("number of images: %" PRIu32 "\n", number_of_images);
-    printf("%x x %x\n\n", width, height);
-    for (int i=0; i < number_of_images; i++)
-        print_image(width, height, ptr, (i*width*height)+4);
+    fread(&number_of_images, sizeof(uint32_t), 1, ptr);
+    number_of_images = swap_endian(number_of_images);
+
+    fread(&height, sizeof(unsigned int), 1, ptr);
+    height = swap_endian(height);
+
+    fread(&width, sizeof(unsigned int), 1, ptr);
+    width = swap_endian(width);
+
+    //printf("magic number: %" PRIu32 "\n", magic_number);
+    //printf("number of images: %" PRIu32 "\n", number_of_images);
+    //printf("%u x %u\n\n", width, height);
+
+    for (int i=0; i < number_of_images; i++) {
+        printf("--- Number %d ---\n", i);
+        print_image(width, height, ptr, (i*width*height));
+    }
 }
 
+
 int main(int argc, char *argv[]) {
     if (argc == 1) {
         printf("Utilisation: %s [FILE]\n", argv[0]);
         return 1;
     }
-    print_bytes(argv[1]);
+    read_mnist_images(argv[1]);
     return 0;
 }