Date: Thu, 16 Apr 2020 12:34:45 -0400 From: 'Rich Felker' <dalias@...c.org> To: sidneym@...eaurora.org Cc: musl@...ts.openwall.com Subject: Re: Hexagon DSP support On Thu, Apr 16, 2020 at 11:26:52AM -0500, sidneym@...eaurora.org wrote: > > > > -----Original Message----- > > From: Rich Felker <dalias@...c.org> > > Sent: Thursday, April 16, 2020 10:34 AM > > To: sidneym@...eaurora.org; musl@...ts.openwall.com > > Subject: Re: [musl] Hexagon DSP support > > > > On Thu, Apr 16, 2020 at 11:36:38AM +0200, Szabolcs Nagy wrote: > > > * sidneym@...eaurora.org <sidneym@...eaurora.org> [2020-04-15 > > 13:22:29 -0500]: > > > > > sqrt/sqrtf should work too (you may want to implement them if > > > > > there is a single instruction) other math failures are not target > specific. > > > > > > > > In fact that does go away if I used the hardware accelerated routine > that > > is > > > > part of compiler-rt.builtins (__hexagon_sqrt) Creating an explicit > > > > reference to compiler-rt-builtins vs just copying the assembly, > > > > which is preferred? > > > > > > the preferred is like on other targets an inline asm block. > > > i think using __builtin_sqrt may be fine too if you know that all > > > hexagon compilers support that and doesnt generate an actual sqrt call > > > (e.g. on gcc that needs -fno-math-errno). > > > > __builtin_sqrt is explicitly allowed to compile to an external call to > sqrt (at > > compiler discretion), and thus can't be used to implement the sqrt > function. > > If you're implementing a native sqrt it should be inline asm. But the C > sqrt > > should work too. If it's not working that indicates a bug in the compiler, > in the > > code in musl, or in qemu, and whichever it is we should track that down > and > > get it fixed. > > I will add the assembly version for sqrt. There was an issue in qemu when > using the assembly version but that is fixed. FWIW when I use the soft > version with clang for hexagon I still see errors, mostly looking for > INEXACT but not seeing it. I saw errors that were actual incorrect results not just wrong exception flags, like: src/math/ucb/sqrt.h:49: RU sqrt(0x1.fffffffffffffp+1023) want 0x1p+512 got 0x1.fffffffffffffp+511 ulperr -0.250 = -0x1p-1 + 0x1p-2 At least they all seemed to be in non-default rounding modes though so the impact is low-ish. These are probably all qemu bugs but hard to say for sure... Rich
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