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TMS320F28384D: Specified behaviour of FRACF32 and FRACF64 instructions for negative inputs

IainRist
Intellectual 711 points
Part Number: TMS320F28384D

The FRACF32 and FRACF64 instructions are documented in TMS320C28x Extended Instruction Sets Technical Reference Manual, pages 59 and 328 of SPRUHS1C respectively .

There are no examples given for a negative input, and the descriptions does not explicitly state the sign bit is copied from source to destination.

Is the behaviour of the FRACF32 and FRAC64 instructions specified for negative inputs?

  • 0
    TI__Expert 5410 points

    Hi,

    Yes the sign carries over as you can see below:

    I passed #-19.625 as input and the output preserves the - sign. However, the instructions do not affect the flags in the STF register. Same applies to FRAC64 too.

    -Shantanu

  • 0 in reply to Shanty
    Intellectual 711 points

    Hi Shantanu,

    Is the result that the sign bit is copied across a specification of current and future behaviour, or only an observation of current behaviour? Will the copying of the sign be maintained on all future iterations of the FPU/FPU64?

    If so, I will request a change to the manual to include the example above.

    - Iain

  • +1 in reply to IainRist
    TI__Expert 5410 points

    Hi Iain,

    The sign bit being copied over has always been the behaviour. There are no plans to change that. 

    Thank you for your inputs. We will make the change.

    -Shantanu