Difference between revisions of "Kernel/RtlExtendedLargeIntegerDivide"

Revision as of 05:49, 17 January 2019

RtlExtendedLargeIntegerDivide will call RtlRaiseStatus(STATUS_INTEGER_DIVIDE_BY_ZERO) if Divisor = 0. Otherwise, a custom binary division algorithm is used to perform the divide operation. The algorithm below was reverse engineered from original hardware.

LARGE_INTEGER quotient = Dividend; ULONG local_remainder = 0; BOOLEAN carry, remainder_carry;

for (uint8_t i = 64; i > 0; i--) {

   carry = (quotient.QuadPart >> 63) & 0x1;
   remainder_carry = (local_remainder >> 31) & 0x1;
   quotient.QuadPart <<= 1;
   local_remainder = (local_remainder << 1) | carry;
   if (remainder_carry || (local_remainder >= Divisor)) {
       quotient.u.LowPart += 1;
       local_remainder -= Divisor;
   }

} if (Remainder) {

   *Remainder = local_remainder;

}