ST20C2 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST20C2

Instruction Set Reference Manual

STMicroelectronics 

xword

xword

extend to word

Code: 23 FA

Description: Sign extend an N-bit signed number in Breg into a full word. To indicate

the value of N, bit N-1 of Areg is set to 1; all other bits must be 0.

Definition:

if (Areg is a not power of 2)

Areg′ ← undefined

else if (Areg = MostNeg)

Areg′ ← Breg

else if (Breg ≥ 0) and (Breg < Areg)

Areg′ ← Breg

else if (Breg ≥ Areg) and ((Breg >> 1) < Areg)

Areg′ ← Breg − (Areg << 1)

else

Areg′ ← undefined

– N is BitsPerWord

– Breg N bits and positive

– Breg N bits and negative

– Breg more than N bits

Breg′ ← Creg

Creg′ ← undefined

Error signals: none

Comments:

Secondary instruction.

See also: xbword xsword

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