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. Nicolas
