Art of Assembly Language, 1st Edition

11.11. 11.11 Merging Bit Strings

Another common bit string operation is producing a single bit string by merging, or interleaving, bits from two different sources. The following example code sequence creates a 32-bit string by merging alternate bits from two 16-bit strings:

// Merge two 16-bit strings into a single 32-bit string.
// AX - Source for even numbered bits.
// BX - Source for odd numbered bits.
// CL - Scratch register.
// EDX- Destination register.

               mov( 16, cl );
MergeLp:       shrd( 1, eax, edx );       // Shift a bit from EAX into EDX.
               shrd( 1, ebx, edx );       // Shift a bit from EBX into EDX.
               dec( cl );
               jne MergeLp;

This particular example merged two 16-bit values together, alternating their bits in the result value. For a faster implementation ...