GCC has the __builtin_clzll builtin function that according to https://www.geeksforgeeks.org/builtin-functions-gcc-compiler/:
__builtin_clz(x): This function is used to count the leading zeros of the integer. Note : clz = count leading zero’s
I think LLVM also has these functions, and Rust is compiled with LLVM. Is there a way to use this function in Rust?
Rust has the leading_zeros method on all built-in integer types. And if compiled on a CPU supporting an efficient hardware leading zeros instruction it will use that:
pub fn foo(n: u32) -> u32 {
n.leading_zeros()
}
rustc -O -C target-cpu=broadwell:
example::foo:
lzcnt eax, edi
ret
rustc -O --target arm-unknown-linux-gnueabihf -C target-cpu=cortex-a76:
example::foo:
clz r0, r0
bx lr