On Mon, Nov 26, 2018 at 06:18:01PM +0800, David Laight wrote: > 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. > I use two commits to complete the implementation of the FPU emulator in this patch set. The handling for (1) case is in another patch, "nds32: support denormalized result through FP emulator". Sorry, the above description may be misleading. > It ought to be possibly for the exception routine to rescale the values, > re-issue the same FP instruction, then scale the result. > > David > I Agree. The scheme is common when dealing with denormalized numbers, including the softfp module of the kernel used in this patchset.
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