Integer Saturation Arithmetic - Cirrus Logic EP93 Series User Manual

MaverickCrunch Co-Processor
EP93xx User's Guide
A double precision value requires all 64 bits:
3
A 32-bit integer is stored in the lower 32 bits of a 64-bit register and sign-extended when
written, provided the UI bit in the DSPSC is clear:
Hence, 32-bit integers may be used directly in calculations with 64-bit integers, which are
stored as:

3.1.5 Integer Saturation Arithmetic

By default, the co-processor treats all 32-bit and 64-bit integers as signed values and
automatically saturates the results of most integer operations and all conversions from
floating-point to integer format. Instructions that may saturate their results are:
• CFADD32 and CFADD64
• CFSUB32 and CFSUB64
• CFMUL32 and CFMUL64
• CFMAC32 and CFMSC32
• CFCVTS32 and CFCVTD32
• CFTRUNCS32 and CFTRUNCD32
This behavior, however, can be altered by setting the UI bit and the ISAT bit in the DSPSC.
With the UI bit clear (the default), 32-bit and 64-bit integer operations are treated as signed
with respect to overflow and underflow detection and saturation as well as compare
operations. Setting the UI bit causes the MaverickCrunch co-processor to treat all 32-bit and
64-bit integer operations as unsigned with respect to overflow, underflow, saturation, and
comparison.
3-4
Opcode
63 62 52 51
Sign Exponent
Opcode
63
Sign Extension
Opcode
63 62
Sign
Copyright 2007 Cirrus Logic
Significand
32 31 30
Sign Data
Data
0
0
0
DS785UM1