RtlCompareMemoryUlong - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTRTL_H

// Memory

_Must_inspect_result_
NTSYSAPI
SIZE_T
NTAPI
RtlCompareMemoryUlong(
    _In_reads_bytes_(Length) PVOID Source,
    _In_ SIZE_T Length,
    _In_ ULONG Pattern
    );

#endif

View code on GitHub

This function is documented in Windows Driver Kit.