Difference between revisions of "Byte/Word Extension"

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Latest revision as of 18:11, 29 August 2019

The Byte/Word eXtensions were first introduced in the EV56 and has been available in all subsequent models. The instructions were provided to reduce the number of instructions for operations such as loading and storing bytes or words to and from memory and sign-extending of byte and word values. According to the Alpha Architecture Handbook [1] it is recommended to use these instructions on platforms where they are present instead of the sequences of extract, mask and insert instructions that would otherwise be needed.

Added Instructions

Mnemonic Description
LDBU Load byte unaligned
LDWU Load word unaligned
SEXTB Sign-extend byte
SEXTW Sign-extend word
STB Store byte
STW Store word

Determining Presence

To determine the presence of BWX, use the amask instruction.