Comment the push int function

src/hbas.c

@@ -110,16 +110,44 @@ size_t label_lookup(LabelVec *labels, char *name, size_t len) {
   return INVALID;
 }
 
-// safety: assumes the buffer has enough place for specified integer size
+// safety: assumes the buffer has enough place for specified integer size.
+// `sign` is a bitset, where bit `1` indicates that value accepts a signed int,
+// and bit `2` indicates that value accepts an unsigned int.
 AsmError push_int_le(char *buf, uint64_t val, size_t size, uint8_t sign) {
-  int valid_uint = val >> (size * 8) == 0;
+  // Unsigned integers must have all upper bits set to zero. To check this,
+  // we shift the value right by the integer size and verify it equals zero.
+  int valid_uint = (val >> (size * 8)) == 0;
+
+  // For signed integers, the sign-extended high bits must match the sign bit.
+  // By shifting right by one less than the total bit size (size * 8 - 1),
+  // we isolate the sign bit and any sign-extended bits. For a value fitting
+  // in the signed range, this operation results in either 0 (for non-negative
+  // values) or -1 (for negative values due to sign extension).
   int64_t int_shifted = ((int64_t)val) >> (size * 8 - 1);
-  int valid_int = int_shifted == 0 || (~int_shifted) == 0;
-  // Note: this assumes the format for `sign` is a bitset.
+
+  // To unify the check for both positive and negative cases, we adjust
+  // non-zero values (-1) by incrementing by 1.  This turns -1 into 0,
+  // enabling a single check for 0 to validate both cases.  This adjustment
+  // simplifies the validation logic, allowing us to use a single condition to
+  // check for proper sign extension or zero extension in the original value.
+  int_shifted += int_shifted != 0;
+
+  // A valid signed integer will have `int_shifted` equal to 0
+  // after adjustment, indicating proper sign extension. 
+  int valid_int = int_shifted == 0;
+
+  // Validity bitmask to represents whether the value
+  // fits as signed, unsigned, or both.
   int validity = valid_int | (valid_uint << 1);
+
+  // If the value's validity doesn't match the `sign` requirements,
+  // we report an overflow.
   if ((validity & sign) == 0) {
     return ErrImmediateOverflow;
   }
+
+  // Write out the bytes of the integer to the buffer in little-endian order,
+  // starting with the lowest byte first.
   for (size_t ii = 0; ii < size; ii += 1) {
     buf[ii] = val & 0xff;
     val >>= 8;