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All single-precision values with the maximum exponent field value and a nonzero fraction field are valid NaNs. A most significant fraction bit of zero indicates a Signaling NaN (SNaN). A one indicates a Quiet NaN (QNaN). Two NaN values are treated as different NaNs if they differ in any bit. Table 3-28 shows the default NaN values.
Sign | Fraction | Fraction |
---|---|---|
0 | 0xFF | bit [22] = 1, bits [21:0] are all zeros |
Processing of input NaNs for Arm® floating-point functionality and libraries is defined as follows:
Table 3-29 summarizes the effects of NaN operands on instruction execution.
Instruction Type | Default NaN Mode | With QNaN Operand | With SNaN Operand |
---|---|---|---|
Arithmetic CDP | Off | The QNaN or one of the QNaN operands, if there is more than one, is returned according to the rules given in the ARMv7-M Architecture Reference Manual. | IOC(1) set. The SNaN is quieted and the result NaN is determined by the rules given in the ARMv7-M Architecture Reference Manual. |
On | Default NaN returns. | IOC(1) set. Default NaN returns. | |
Non-arithmetic CDP | Off | NaN passes to destination with sign changed as appropriate. | |
On | |||
FCMP(Z) | – | Unordered compare. | IOC set. Unordered compare. |
– | IOC set. Unordered compare. | IOC set. Unordered compare. | |
Load/store | Off | All NaNs transferred. | |
On |