<div dir="ltr"><div class="gmail_quote"><div dir="ltr">On Tue, Nov 13, 2018 at 3:21 PM Roland Scheidegger <<a href="mailto:sroland@vmware.com">sroland@vmware.com</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Am 12.11.18 um 20:40 schrieb Jason Ekstrand: > On Mon, Nov 12, 2018 at 1:29 PM Christian Gmeiner > <<a href="mailto:christian.gmeiner@gmail.com" target="_blank">christian.gmeiner@gmail.com</a> <mailto:<a href="mailto:christian.gmeiner@gmail.com" target="_blank">christian.gmeiner@gmail.com</a>>> wrote: > > Hi Jason > > Am Sa., 1. Sep. 2018 um 21:23 Uhr schrieb Jason Ekstrand > <<a href="mailto:jason@jlekstrand.net" target="_blank">jason@jlekstrand.net</a> <mailto:<a href="mailto:jason@jlekstrand.net" target="_blank">jason@jlekstrand.net</a>>>: > > > > 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). </blockquote><div> </div><div>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.</div><div> </div><div>--Jason </div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Roland > > Reviewed-by: Jason Ekstrand <<a href="mailto:jason@jlekstrand.net" target="_blank">jason@jlekstrand.net</a> > <mailto:<a href="mailto:jason@jlekstrand.net" target="_blank">jason@jlekstrand.net</a>>> > > > > On September 1, 2018 14:16:11 Christian Gmeiner > > <<a href="mailto:christian.gmeiner@gmail.com" target="_blank">christian.gmeiner@gmail.com</a> <mailto:<a href="mailto:christian.gmeiner@gmail.com" target="_blank">christian.gmeiner@gmail.com</a>>> > wrote: > > > > > Signed-off-by: Christian Gmeiner <<a href="mailto:christian.gmeiner@gmail.com" target="_blank">christian.gmeiner@gmail.com</a> > <mailto:<a href="mailto:christian.gmeiner@gmail.com" target="_blank">christian.gmeiner@gmail.com</a>>> > > > --- > > > 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 > > > <a href="mailto:mesa-dev@lists.freedesktop.org" target="_blank">mesa-dev@lists.freedesktop.org</a> > <mailto:<a href="mailto:mesa-dev@lists.freedesktop.org" target="_blank">mesa-dev@lists.freedesktop.org</a>> > > > <a href="https://lists.freedesktop.org/mailman/listinfo/mesa-dev" rel="noreferrer" target="_blank">https://lists.freedesktop.org/mailman/listinfo/mesa-dev</a> > <<a href="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" rel="noreferrer" target="_blank">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</a>> > > > > > > > > -- > greets > -- > Christian Gmeiner, MSc > > <a href="https://christian-gmeiner.info" rel="noreferrer" target="_blank">https://christian-gmeiner.info</a> > <<a href="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" rel="noreferrer" target="_blank">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</a>> > > > _______________________________________________ > mesa-dev mailing list > <a href="mailto:mesa-dev@lists.freedesktop.org" target="_blank">mesa-dev@lists.freedesktop.org</a> > <a href="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" rel="noreferrer" target="_blank">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</a> > </blockquote></div></div>