From d81f2c0509e001a77c572200219ceb03563d1b61 Mon Sep 17 00:00:00 2001
From: Vincent Pelletier <plr.vincent@gmail.com>
Date: Sat, 22 Oct 2022 03:00:59 +0000
Subject: [PATCH] NES.ino: Simplify CRC functions.

It seems crc32EEP only exists because the actual number of bytes read from
file were not checked, hence falling back to smaller reads.
Instead, always read up to the full available buffer, adding to the CRC
only as many bytes as were actually read.
Also, move some related variables to local scope.
Overall, this saves about 50 bytes of code and 80 bytes of global ram.
---
 Cart_Reader/NES.ino | 60 ++++++++++++++-------------------------------
 1 file changed, 18 insertions(+), 42 deletions(-)

diff --git a/Cart_Reader/NES.ino b/Cart_Reader/NES.ino
index de72358..bb3e697 100644
--- a/Cart_Reader/NES.ino
+++ b/Cart_Reader/NES.ino
@@ -1458,45 +1458,21 @@ int int_pow(int base, int exp) {  // Power for int
 /******************************************
    CRC Functions
  *****************************************/
-FsFile crcFile;
-char tempCRC[9];
 
-uint32_t crc32(FsFile& file, uint32_t& charcnt) {
-  uint32_t oldcrc32 = 0xFFFFFFFF;
-  charcnt = 0;
-  while (file.available()) {
-    crcFile.read(sdBuffer, 512);
-    for (int x = 0; x < 512; x++) {
-      uint8_t c = sdBuffer[x];
-      charcnt++;
-      oldcrc32 = updateCRC(c, oldcrc32);
-    }
-  }
-  return ~oldcrc32;
-}
-
-uint32_t crc32EEP(FsFile& file, uint32_t& charcnt) {
-  uint32_t oldcrc32 = 0xFFFFFFFF;
-  charcnt = 0;
-  while (file.available()) {
-    crcFile.read(sdBuffer, 128);
-    for (int x = 0; x < 128; x++) {
-      uint8_t c = sdBuffer[x];
-      charcnt++;
-      oldcrc32 = updateCRC(c, oldcrc32);
-    }
-  }
-  return ~oldcrc32;
-}
-
-void calcCRC(char* checkFile, unsigned long filesize, uint32_t* crcCopy, unsigned long offset) {
-  uint32_t crc;
-  crcFile = sd.open(checkFile);
+void calcCRC(char* checkFile, uint32_t* crcCopy, unsigned long offset) {
+  uint32_t crc = 0xFFFFFFFF;
+  char tempCRC[9];
+  int byte_count;
+  FsFile crcFile = sd.open(checkFile);
   crcFile.seek(offset);
-  if (filesize < 1024)
-    crc = crc32EEP(crcFile, filesize);
-  else
-    crc = crc32(crcFile, filesize);
+  while (crcFile.available()) {
+    byte_count = crcFile.read(sdBuffer, sizeof(sdBuffer));
+    for (int x = 0; x < byte_count; x++) {
+      uint8_t c = sdBuffer[x];
+      crc = updateCRC(c, crc);
+    }
+  }
+  crc = ~crc;
   crcFile.close();
   sprintf(tempCRC, "%08lX", crc);
 
@@ -1753,7 +1729,7 @@ void outputNES() {
   println_Msg(F(""));
   display_Update();
 
-  calcCRC(outputFile, (prg + chr) * 1024, NULL, crcOffset);
+  calcCRC(outputFile, NULL, crcOffset);
   LED_RED_OFF;
   LED_GREEN_OFF;
   LED_BLUE_OFF;
@@ -3671,7 +3647,7 @@ void readPRG(boolean readrom) {
       println_Msg(F(""));
       display_Update();
 #ifndef nointro
-      calcCRC(fileName, prg * 1024, &prg_crc32, 0);
+      calcCRC(fileName, &prg_crc32, 0);
 #endif
     }
   }
@@ -4396,7 +4372,7 @@ void readCHR(boolean readrom) {
         println_Msg(F(""));
         display_Update();
 #ifndef nointro
-        calcCRC(fileName, chr * 1024, &chr_crc32, 0);
+        calcCRC(fileName, &chr_crc32, 0);
 #endif
       }
     }
@@ -4585,9 +4561,9 @@ void readRAM() {
       display_Update();
 
       if ((mapper == 16) || (mapper == 159))
-        calcCRC(fileName, eepsize, NULL, 0);
+        calcCRC(fileName, NULL, 0);
       else
-        calcCRC(fileName, ram * 1024, NULL, 0);
+        calcCRC(fileName, NULL, 0);
     }
   }
   set_address(0);