# _lzcnt_u32/64

Counts the number of leading zero bits in a source operand. Returns operand size as output when source operand is zero. The corresponding Intel® AVX2 instruction is LZCNT.

## Syntax

extern unsigned int _lzcnt_u32(unsigned int source);

extern unsigned __int64 _lzcnt_u64(unsigned __int64 source);

## Arguments

source | the source operand used for the operation

## Description

Counts the number of leading most significant zero bits in a source operand returning the result into a destination when source operand is 0.

## Returns

Result of the operation.

Parent topic: Intrinsics for Operations to Manipulate Integer Data at Bit-Granularity