On Fri, 27 Jul 2018, Nicolas Pitre wrote: > On Fri, 27 Jul 2018, Wilco Dijkstra wrote: > > > Hi Nicolas, > > > > I think your patch doesn't quite work as expected: > > > > @@ -238,9 +238,10 @@ LSYM(Lad_a): > > movs ip, ip, lsl #1 > > adcs xl, xl, xl > > adc xh, xh, xh > > - tst xh, #0x00100000 > > - sub r4, r4, #1 > > - bne LSYM(Lad_e) > > + subs r4, r4, #1 > > + do_it hs > > + tsths xh, #0x00100000 > > + bhi LSYM(Lad_e) > > > > If the exponent in r4 is zero, the carry bit will be clear, so we don't > > execute the tsths > > and fallthrough (the denormal will be normalized and then denormalized > > again, but > > that's so rare it doesn't matter really). > > And that's what is intended. > > > However if r4 is non-zero, the carry will be set, and the tsths will be > > executed. This > > clears the carry and sets the Z flag based on bit 20. > > No, not at all. The carry is not affected. And that's the point of the > tst instruction here rather than a cmp: it sets the N and Z flags but > leaves C alone as there is no shifter involved.
That being said, a cmp as you suggested would have worked too (with the bhi changed to bhs). But the patch as is produces the same behavior. Nicolas
