Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH v4 2/5] nds32: Support FP emulation | Date | Mon, 26 Nov 2018 10:18:01 +0000 |
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From: Vincent Chen > Sent: 26 November 2018 01:23 > On Fri, Nov 23, 2018 at 06:53:37PM +0800, David Laight wrote: > > From: Vincent Chen > > > Sent: 22 November 2018 03:15 > > > > > > The Andes FPU coprocessor does not support denormalized number handling. > > > According to the specification, FPU generates a denorm input exception > > > that requires the kernel to deal with this instrution operation when it > > > encounters denormalized operands. Hence an nds32 FPU ISA emulator in the > > > kernel is required to meet requirement. > > > > What does the FPU generate for results near zero? > > 1. The calculation result is a denormalized number > Depending on the state of underflow trap, the FPU will raise an underflow > exception or flash the result to zero. > > 2. One of the operands is a denormalized number > Depending on the state of the flash-to-zero mode, the FPU will raise a > denormalized input exception, which is a specific exception of the nds FPU, > or directly treats the operand as 0.
You didn't mention (1) in the commit message.
It ought to be possibly for the exception routine to rescale the values, re-issue the same FP instruction, then scale the result.
David
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