Encoding:

Format:

SEB rt, rs

Purpose:

Sign-Extend Byte

To sign-extend the least significant byte of GPR rs and store the value into GPR rt.

Description:

 GPR[rt] = SignExtend(GPR[rs]7..0)

The least significant byte from GPR rs is sign-extended and stored in GPR rt.

Restrictions:

Prior to architecture Release 2, this instruction resulted in a Reserved Instruction exception.

If GPR rs does not contain a sign-extended 32-bit value (bits 63..31 equal), then the result of the operation is

UNPREDICTABLE.

Operation:

if NotWordValue(GPR[rs]) then
   UNPREDICTABLE
endif
GPR[rt] = sign_extend(GPR[rs]7..0)

Exceptions:

Reserved Instruction

Programming Notes:

For symmetry with the SEB and SEH instructions, you expect that there would be ZEB and ZEH instructions that zero-extend the source operand and expect that the SEW and ZEW instructions would exist to sign- or zero-extend a word to a doubleword. These instructions do not exist because there are functionally-equivalent instructions already in the instruction set. The following table shows the instructions providing the equivalent functions.

Expected InstructionFunctionEquivalent Instruction

Zero-Extend Byte

            ZEB rx,ry                          ANDI rx,ry,0xFF 

Zero-Extend Halfword

            ZEH rx,ry                         ANDI rx,ry,0xFFFF

Sign-Extend Word

            SEW rx,ry                            SLL rx,ry,0
           ZEW rx,rx1Zero-Extend Word

                                             DINSP32 rx,r0,32,32

1. The equivalent instruction uses rx for both source and destination, so the expected instruction is limited to one register