On Tue, Nov 13, 2018 at 3:21 PM Roland Scheidegger <srol...@vmware.com> wrote:
> Am 12.11.18 um 20:40 schrieb Jason Ekstrand: > > On Mon, Nov 12, 2018 at 1:29 PM Christian Gmeiner > > <christian.gmei...@gmail.com <mailto:christian.gmei...@gmail.com>> > wrote: > > > > Hi Jason > > > > Am Sa., 1. Sep. 2018 um 21:23 Uhr schrieb Jason Ekstrand > > <ja...@jlekstrand.net <mailto:ja...@jlekstrand.net>>: > > > > > > I don't think either of these work for negative numbers > > > > > > > I would like to land this patch - can you provide some details why > > this does not work for > > negative numbers? > > > > > > No, this is correct. It's GLSL's definition of fract(x) that's dumb. > > GLSL defines fract(x) as x - floor(x) (exactly what your formula says. > > This means that > > > > fract(-1.4) = -1.4 - floor(-1.4) = -1.4 - (-2.0) = -1.4 + 2.0 = 0.6 > > > > so GLSL fract() doesn't give you the fractional part at all. *sigh* > Can you elaborate why you think this result to be wrong? In fact it's > the only definition I've ever heard of. But yes, wikipedia says fract > for negative numbers is open for debate (with 3 possible solutions). In > the context of graphics shading languages, it is however most definitely > the agreed-upon formula for fractional parts (and certainly the same > formula was used pre-glsl or hlsl). > It falls into exactly the same category as all the different ways to define modulus/remainder. You just sort-of end up having to pick one. I guess my main gripe is that, when someone says "returns the fractional part", I would expect x = trunc(x) + fract(x) or x = trunc(x) + sign(x) * fract(x). Of the possible conventions, they chose the one that I find to be the strangest. That's all. --Jason > Roland > > > > > > Reviewed-by: Jason Ekstrand <ja...@jlekstrand.net > > <mailto:ja...@jlekstrand.net>> > > > > > > > On September 1, 2018 14:16:11 Christian Gmeiner > > > <christian.gmei...@gmail.com <mailto:christian.gmei...@gmail.com>> > > wrote: > > > > > > > Signed-off-by: Christian Gmeiner <christian.gmei...@gmail.com > > <mailto:christian.gmei...@gmail.com>> > > > > --- > > > > src/compiler/nir/nir.h | 3 +++ > > > > src/compiler/nir/nir_opt_algebraic.py | 1 + > > > > 2 files changed, 4 insertions(+) > > > > > > > > diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h > > > > index 169fa1fa20..d81eefc032 100644 > > > > --- a/src/compiler/nir/nir.h > > > > +++ b/src/compiler/nir/nir.h > > > > @@ -2054,6 +2054,9 @@ typedef struct nir_shader_compiler_options > { > > > > */ > > > > bool fdot_replicates; > > > > > > > > + /** lowers ffloor to fsub+ffract: */ > > > > + bool lower_ffloor; > > > > + > > > > /** lowers ffract to fsub+ffloor: */ > > > > bool lower_ffract; > > > > > > > > diff --git a/src/compiler/nir/nir_opt_algebraic.py > > > > b/src/compiler/nir/nir_opt_algebraic.py > > > > index ae1261f874..3d2b861a42 100644 > > > > --- a/src/compiler/nir/nir_opt_algebraic.py > > > > +++ b/src/compiler/nir/nir_opt_algebraic.py > > > > @@ -118,6 +118,7 @@ optimizations = [ > > > > (('~flrp', a, 0.0, c), ('fadd', ('fmul', ('fneg', a), c), a)), > > > > (('flrp@32', a, b, c), ('fadd', ('fmul', c, ('fsub', b, a)), > a), > > > > 'options->lower_flrp32'), > > > > (('flrp@64', a, b, c), ('fadd', ('fmul', c, ('fsub', b, a)), > a), > > > > 'options->lower_flrp64'), > > > > + (('ffloor', a), ('fsub', a, ('ffract', a)), > > 'options->lower_ffloor'), > > > > (('ffract', a), ('fsub', a, ('ffloor', a)), > > 'options->lower_ffract'), > > > > (('~fadd', ('fmul', a, ('fadd', 1.0, ('fneg', ('b2f', c)))), > > ('fmul', b, > > > > ('b2f', c))), ('bcsel', c, b, a), 'options->lower_flrp32'), > > > > (('~fadd@32', ('fmul', a, ('fadd', 1.0, ('fneg', c > > ))), ('fmul', b, > > > > c )), ('flrp', a, b, c), '!options->lower_flrp32'), > > > > -- > > > > 2.17.1 > > > > > > > > _______________________________________________ > > > > mesa-dev mailing list > > > > mesa-dev@lists.freedesktop.org > > <mailto:mesa-dev@lists.freedesktop.org> > > > > https://lists.freedesktop.org/mailman/listinfo/mesa-dev > > < > https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.freedesktop.org%2Fmailman%2Flistinfo%2Fmesa-dev&data=02%7C01%7Csroland%40vmware.com%7Ce0fe2529778847ca3ef208d648d6bb83%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636776484451503870&sdata=vkUGCDEE3AeUCdZaibTXfuIwQS0FU39C3V%2FnJMraRlM%3D&reserved=0 > > > > > > > > > > > > > > > -- > > greets > > -- > > Christian Gmeiner, MSc > > > > https://christian-gmeiner.info > > < > https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fchristian-gmeiner.info&data=02%7C01%7Csroland%40vmware.com%7Ce0fe2529778847ca3ef208d648d6bb83%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636776484451513879&sdata=IPMIs3gEGPgunAgWAoMjjR%2Bev%2FEBADnfJItCHtFuyYc%3D&reserved=0 > > > > > > > > _______________________________________________ > > mesa-dev mailing list > > mesa-dev@lists.freedesktop.org > > > https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.freedesktop.org%2Fmailman%2Flistinfo%2Fmesa-dev&data=02%7C01%7Csroland%40vmware.com%7Ce0fe2529778847ca3ef208d648d6bb83%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C1%7C0%7C636776484451523879&sdata=uioIRixNYHv8b%2FKTa%2BXqkzkDVZCnlm4FYdzsnxsDo38%3D&reserved=0 > > > >
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