Fisherman166 at 05:51, 17 January 2019

2019-01-17T05:51:20Z

Fisherman166: Add binary division algorithm

2019-01-17T05:49:59Z

Add binary division algorithm

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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;
}

@@ Line 1: / Line 1: @@
 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;
+    LARGE_INTEGER quotient = Dividend;
-ULONG local_remainder = 0;
+    ULONG local_remainder = 0;
-BOOLEAN carry, remainder_carry;
+    BOOLEAN carry, remainder_carry;
+    for (uint8_t i = 64; i > 0; i--) {
-for (uint8_t i = 64; i > 0; i--) {
+        carry = (quotient.QuadPart >> 63) & 0x1;
-    carry = (quotient.QuadPart >> 63) & 0x1;
+        remainder_carry = (local_remainder >> 31) & 0x1;
-    remainder_carry = (local_remainder >> 31) & 0x1;
+        quotient.QuadPart <<= 1;
-    quotient.QuadPart <<= 1;
+        local_remainder = (local_remainder << 1) | carry;
-    local_remainder = (local_remainder << 1) | carry;
+        if (remainder_carry || (local_remainder >= Divisor)) {
-    if (remainder_carry || (local_remainder >= Divisor)) {
+            quotient.u.LowPart += 1;
-        quotient.u.LowPart += 1;
+            local_remainder -= Divisor;
-        local_remainder -= Divisor;
+     }

Kernel/RtlExtendedLargeIntegerDivide - Revision history

Fisherman166 at 05:51, 17 January 2019

Fisherman166: Add binary division algorithm