[apps/sequence][apps/graph] Reimplement checksum to avoid risking

overflowing the stack

Change-Id: Ia2b70ceb174d70c20b0e7d635183a890629e4b24

apps/shared/function.cpp

@@ -1,6 +1,7 @@
 #include "function.h"
 #include <string.h>
 #include <math.h>
+#include <assert.h>
 
 using namespace Poincare;
 
@@ -25,6 +26,14 @@ Function& Function::operator=(const Function& other) {
   return *this;
 }
 
+uint32_t Function::checksum() {
+  size_t dataLengthInBytes = TextField::maxBufferSize()*sizeof(char);
+  assert((dataLengthInBytes & 0x3) == 0); // Assert that dataLengthInBytes is a multiple of 4
+  char data[TextField::maxBufferSize()] = {};
+  strlcpy(data, m_text, TextField::maxBufferSize());
+  return Ion::crc32((uint32_t *)data, dataLengthInBytes>>2);
+}
+
 void Function::setContent(const char * c) {
   strlcpy(m_text, c, sizeof(m_text));
   if (m_layout != nullptr) {