Section 6 Floating-Point Unit (FPU)
Rev.1.00 Dec. 13, 2005 Page 141 of 1286
REJ09B0158-0100
6.4 Rounding
In a floating-point instruction, rounding is performed when generating the final operation result
from the intermediate result. Therefore, the result of combination instructions such as FMAC,
FTRV, and FIPR will differ from the result when using a basic instruction such as FADD, FSUB,
or FMUL. Rounding is performed once in FMAC, but twice in FADD, FSUB, and FMUL.
Which of the two rounding methods is to be used is determined by the RM bits in FPSCR.
FPSCR.RM[1:0] = 00: Round to Nearest
FPSCR.RM[1:0] = 01: Round to Zero
Round to Nearest: The operation result is rounded to the nearest expressible value. If there are
two nearest expressible values, the one with an LSB of 0 is selected.
If the unrounded value is 2
Emax
(2 – 2
–P
) or more, the result will be infinity with the same sign as the
unrounded value. The values of Emax and P, respectively, are 127 and 24 for single-precision, and
1023 and 53 for double-precision.
Round to Zero: The digits below the round bit of the unrounded value are discarded.
If the unrounded value is larger than the maximum expressible absolute value, the value will
become the maximum expressible absolute value with the same sign as unrounded value.
Summary of Contents for SH7780 Series
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Page 82: ...Section 1 Overview Rev 1 00 Dec 13 2005 Page 32 of 1286 REJ09B0158 0100 ...
Page 122: ...Section 3 Instruction Set Rev 1 00 Dec 13 2005 Page 72 of 1286 REJ09B0158 0100 ...
Page 146: ...Section 4 Pipelining Rev 1 00 Dec 13 2005 Page 96 of 1286 REJ09B0158 0100 ...
Page 196: ...Section 6 Floating Point Unit FPU Rev 1 00 Dec 13 2005 Page 146 of 1286 REJ09B0158 0100 ...
Page 292: ...Section 9 L Memory Rev 1 00 Dec 13 2005 Page 242 of 1286 REJ09B0158 0100 ...
Page 492: ...Section 12 DDR SDRAM Interface DDRIF Rev 1 00 Dec 13 2005 Page 442 of 1286 REJ09B0158 0100 ...
Page 674: ...Section 15 Clock Pulse Generator CPG Rev 1 00 Dec 13 2005 Page 624 of 1286 REJ09B0158 0100 ...
Page 692: ...Section 16 Watchdog Timer and Reset Rev 1 00 Dec 13 2005 Page 642 of 1286 REJ09B0158 0100 ...
Page 726: ...Section 18 Timer Unit TMU Rev 1 00 Dec 13 2005 Page 676 of 1286 REJ09B0158 0100 ...
Page 1032: ...Section 25 Audio Codec Interface HAC Rev 1 00 Dec 13 2005 Page 982 of 1286 REJ09B0158 0100 ...
Page 1150: ...Section 28 General Purpose I O GPIO Rev 1 00 Dec 13 2005 Page 1100 of 1286 REJ09B0158 0100 ...
Page 1184: ...Section 29 User Break Controller UBC Rev 1 00 Dec 13 2005 Page 1134 of 1286 REJ09B0158 0100 ...
Page 1266: ...Section 31 Electrical Characteristics Rev 1 00 Dec 13 2005 Page 1216 of 1286 REJ09B0158 0100 ...
Page 1328: ...Appendix Rev 1 00 Dec 13 2005 Page 1278 of 1286 REJ09B0158 0100 ...
Page 1336: ...Rev 1 00 Dec 13 2005 Page 1286 of 1286 REJ09B0158 0100 ...
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