##bfm_execute
bits(datasize) dst = if inzero then Zeros(64) else X[d];
bits(datasize) src = X[n];

// perform bitfield move on low bits
bits(datasize) bot = (dst AND NOT(wmask)) OR (ROR(src, R) AND wmask);

// determine extension bits (sign, zero or dest register)
bits(datasize) top = if extend then Replicate(src<S>) else dst;

// combine extension bits and result bits
X[d] = (top AND NOT(tmask)) OR (bot AND tmask);
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