cpopw
Count set bits in word
This instruction is defined by:
Synopsis
This instructions counts the number of 1’s (i.e., set bits) in the least-significant word of the source register.
Software Hint
This operations is known as population count, popcount, sideways sum, bit summation, or Hamming weight. The GCC builtin function `__builtin_popcount (unsigned int x)` is implemented by cpop on RV32 and by cpopw on RV64. The GCC builtin function `__builtin_popcountl (unsigned long x)` for LP64 is implemented by cpop on RV64.
Execution
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Pruned, XLEN == 64
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Original
if ((%%LINK%csr_field;misa.B;CSR[misa].B%% == 1'b0)) {
%%LINK%func;raise;raise%%(ExceptionCode::IllegalInstruction, %%LINK%func;mode;mode%%(), $encoding);
}
XReg bitcount = 0;
XReg rs1_val = X[rs1];
for (U32 i = 0; true; i++) {
if (rs1_val[i] == 1'b1) {
bitcount = bitcount + 1;
}
}
X[rd] = bitcount;if (%%LINK%func;implemented?;implemented?%%(ExtensionName::B) && (%%LINK%csr_field;misa.B;CSR[misa].B%% == 1'b0)) {
%%LINK%func;raise;raise%%(ExceptionCode::IllegalInstruction, %%LINK%func;mode;mode%%(), $encoding);
}
XReg bitcount = 0;
XReg rs1_val = X[rs1];
for (U32 i = 0; i < 32; i++) {
if (rs1_val[i] == 1'b1) {
bitcount = bitcount + 1;
}
}
X[rd] = bitcount;