__ffs

Applicability

Function Usage

Searches for the position of the first bit whose value is 1 in the binary representation of the input data starting from the least significant bit and returns the index of the position. The index starts from 1. If there is no 1 in the binary data, 0 is returned.

Prototype

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int __ffs(int x)

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int __ffs(long long x)

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int __ffs(long x)

Parameters

Returns

The position of the first bit whose value is 1 in the binary representation of the input data starting from the least significant bit.

• If x is 0, the return value is 0.
• If x is 1, the return value is 1.

Restrictions

For SIMT programming, this API is not supported.

Header File to Be Included

To use this API, the simt_api/device_functions.h header file must be included.

Examples

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__simt_vf__ __launch_bounds__(1024) inline void KernelFfs(__gm__ int* dst, __gm__ int* x)
{
    int idx = threadIdx.x + blockIdx.x * blockDim.x;
    dst[idx] = __ffs(x[idx]);
}

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__simt_vf__ __launch_bounds__(1024) inline void KernelFfs(__gm__ int* dst, __gm__ long long* x)
{
    int idx = threadIdx.x + blockIdx.x * blockDim.x;
    dst[idx] = __ffs(x[idx]);
}