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4.6 Byte Manipulation Instructions
Alpha implementations that support the BWX extension provide the following instructions for loading,
Instruction | Meaning | Described in Section |
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LDBU/LDWU | Load byte/word unaligned | 4.2.2 |
SEXTB/SEXTW | 4.6.5 | |
STB/STW | Store byte/word | 4.2.6 |
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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
Table
Mnemonic | Operation |
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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 |
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Instruction Descriptions