Data Bit Expansion

The important item to remember is that with regular data expansion, the enlarging of the data size from a lower bit count to a higher bit count of an unsigned number only requires a 128-bit value of zero. This needs to be interlaced with the value and when the bit size is doubled, a zero is in effect, moved into the upper bits. When working with signed values, instructions such as those that follow are needed so that the sign bit is replicated into the upper bits. Note the size differential in the following diagrams. A data element is being doubled in size: to word from byte or dword from word. Also, a possible change in sign may occur, which is denoted with a from/to ().

CBW Convert Signed AL (Byte) to AX (Word)

CWDE Convert Signed AX (Word) to EAX (DWord)

CDQE Convert Signed EAX (DWord) to RAX (QWord)

Mnemonic

P

PII

K6

3D!

3Mx+

SSE

SSE2

A64

SSE3

E64T

CBW