Incorrect return values for APFloat::convertFromString?

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1

I noticed some odd behavior with APFloat’s convertFromString method.

  1. If I pass the hex representation of the closest value to 0.1 (0x19999Ap-24), everything is fine and opOk is returned. However, if I pass the same value as a decimal string (0.10000002384185791015625), opInexact is set.

  2. On the lower end of the scale, the smallest denormal 0x1p-149 returns opOk, but the slightly larger value 0x1.8p-149 has opUnderflow set and (as expected) opInexact.

Is this behavior correct?

2

Well, they are not the same value. The decimal string depends on the
mantissa size and the rounding mode. For the hex version, only the
mantissa size has to be large enough to not require truncation/rounding.

Joerg

3

The mantissa size is specified at initialization of the APFloat and the rounding mode shouldn't matter in determining *if* a value was rounded. The strings themselves are exact representations of the same value.