Setting Computational Modes
2-14
ADSP-2126x SHARC Processor Hardware Reference
40-Bit Floating-Point Format
When in extended-precision mode (
RND32
bit=0), the DSP supports a
40-bit extended-precision floating-point mode, which has eight additional
LSBs of the mantissa and is compliant with the 754/854 standards. How-
ever, results in this format are more precise than the IEEE single-precision
standard specifies. Extended-precision floating-point data uses a 31-bit
mantissa with a 8-bit exponent plus sign bit.
16-Bit Floating-Point Format (Short Word)
The DSP supports a 16-bit floating-point storage format and provides
instructions that convert the data for 40-bit computations. The 16-bit
floating-point format uses an 11-bit mantissa with a 4-bit exponent plus
sign bit. The 16-bit data goes into bits 23 through 8 of a data register.
Two shifter instructions,
Fpack
and
Funpack
, perform the packing and
unpacking conversions between 32-bit floating-point words and 16-bit
floating-point words. The
Fpack
instruction converts a 32-bit IEEE float-
ing-point number in a data register into a 16-bit floating-point number.
Funpack
converts a 16-bit floating-point number in a data register to a
32-bit IEEE floating-point number. Each instruction executes in a single
cycle.
When 16-bit data is written to bits 23 through 8 of a data register, the
DSP automatically extends the data into a 32-bit integer (bits 39 through
8). If the
SSE
bit in
MODE1
is set (1), the DSP sign extends the upper 16
bits. If the
SSE
bit is cleared (0), the DSP zeros the upper 16 bits.
The 16-bit floating-point format supports gradual underflow. This
method sacrifices precision for dynamic range. When packing a number
that would have underflowed, the exponent clears to zero and the mantissa
(including a “hidden” 1) right-shifts the appropriate amount. The packed
result is a denormal, which can be unpacked into a normal IEEE float-
ing-point number.
Summary of Contents for ADSP-21261 SHARC
Page 30: ...Contents xxx ADSP 2126x SHARC Processor Hardware Reference ...
Page 40: ...Register Diagram Conventions xl ADSP 2126x SHARC Processor Hardware Reference ...
Page 58: ...Differences From Previous SHARCs 1 18 ADSP 2126x SHARC Processor Hardware Reference ...
Page 112: ...Secondary Processing Element PEy 2 54 ADSP 2126x SHARC Processor Hardware Reference ...
Page 178: ...Summary 3 66 ADSP 2126x SHARC Processor Hardware Reference ...
Page 204: ...DAG Instruction Summary 4 26 ADSP 2126x SHARC Processor Hardware Reference ...
Page 322: ...Setting Up DMA 7 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 436: ...SPORT Programming Examples 9 86 ADSP 2126x SHARC Processor Hardware Reference ...
Page 521: ...ADSP 2126x SHARC Processor Hardware Reference 11 31 Input Data Port rts IDP_ISR end ...
Page 522: ...Input Data Port Programming Example 11 32 ADSP 2126x SHARC Processor Hardware Reference ...
Page 590: ...Timer Programming Examples 14 20 ADSP 2126x SHARC Processor Hardware Reference ...
Page 796: ...I O Processor Registers A 174 ADSP 2126x SHARC Processor Hardware Reference ...
Page 800: ...B 4 ADSP 2126x SHARC Processor Core Manual ...
Page 846: ...Index I 36 ADSP 2126x SHARC Processor Hardware Reference ...