Compaq ECQD2KCTE manual Byte Manipulation Instructions, Instruction Meaning Described in Section

4.6 Byte Manipulation Instructions

Alpha implementations that support the BWX extension provide the following instructions for loading, sign-extending, and storing bytes and words between a register and memory:

Instruction	Meaning	Described in Section
LDBU/LDWU	Load byte/word unaligned	4.2.2
SEXTB/SEXTW	Sign-extend byte/word	4.6.5
STB/STW	Store byte/word	4.2.6

The AMASK instruction reports whether a particular Alpha implementation supports the BWX extension. AMASK is described in Sections 4.11.1 and D.3.

LDBU and STB are the recommended way to perform byte load and store operations on Alpha implementations that support them; use them rather than the extract, insert, and mask byte instructions described in this section. In particular, the implementation examples in this sec- tion that illustrate byte operations are not appropriate for Alpha implementations that support the BWX extension – instead use the recommendations in Section A.4.1.

In addition to LDBU and STB, Alpha provides the instructions in Table 4–7for operating on byte operands within registers.

Table 4–7: Byte-Within-Register Manipulation Instructions Summary

Mnemonic	Operation
CMPBGE	Compare Byte
EXTBL	Extract Byte Low
EXTWL	Extract Word Low
EXTLL	Extract Longword Low
EXTQL	Extract Quadword Low
EXTWH	Extract Word High
EXTLH	Extract Longword High
EXTQH	Extract Quadword High
INSBL	Insert Byte Low
INSWL	Insert Word Low
INSLL	Insert Longword Low
INSQL	Insert Quadword Low

Instruction Descriptions 4–47