[Mesa-dev] [PATCH] util/format: Fix clamping to 32bit integers.
From: José Fonseca Use clamping constants that guarantee no integer overflows. As spotted by Chris Forbes. This causes the code to change as: - value |= (uint32_t)CLAMP(src[0], 0.0f, 4294967295.0f); + value |= (uint32_t)CLAMP(src[0], 0.0f, 4294967040.0f); - value |= (uint32_t)((int32_t)CLAMP(src[0], -2147483648.0f, 2147483647.0f)); + value |= (uint32_t)((int32_t)CLAMP(src[0], -2147483648.0f, 2147483520.0f)); --- src/gallium/auxiliary/util/u_format_pack.py | 27 +++ 1 file changed, 27 insertions(+) diff --git a/src/gallium/auxiliary/util/u_format_pack.py b/src/gallium/auxiliary/util/u_format_pack.py index 90f348e..d5138cc 100644 --- a/src/gallium/auxiliary/util/u_format_pack.py +++ b/src/gallium/auxiliary/util/u_format_pack.py @@ -207,9 +207,36 @@ def get_one_shift(type): assert False +def truncate_mantissa(x, bits): +'''Truncate an integer so it can be represented exactly with a floating +point mantissa''' + +assert isinstance(x, (int, long)) + +s = 1 +if x < 0: +s = -1 +x = -x + +# We can represent integers up to mantissa + 1 bits exactly +mask = (1 << (bits + 1)) - 1 + +# Slide the mask until the MSB matches +shift = 0 +while (x >> shift) & ~mask: +shift += 1 + +x &= mask << shift +x *= s +return x + + def value_to_native(type, value): '''Get the value of unity for this type.''' if type.type == FLOAT: +if type.size <= 32 \ +and isinstance(value, (int, long)): +return truncate_mantissa(value, 23) return value if type.type == FIXED: return int(value * (1 << (type.size/2))) -- 1.9.1 ___ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
Re: [Mesa-dev] [PATCH] util/format: Fix clamping to 32bit integers.
Looks good to me though I barely understand the code there... I guess ideally you'd generate code which actually clamps to the max int value representable instead, but that probably would get even more messy (something like: val = MAX(src[0], -2147483648.0f) if (src[0] >= 2147483648.0f) val = 2147483647) Reviewed-by: Roland Scheidegger Am 07.11.2014 um 22:25 schrieb jfons...@vmware.com: > From: José Fonseca > > Use clamping constants that guarantee no integer overflows. > > As spotted by Chris Forbes. > > This causes the code to change as: > > - value |= (uint32_t)CLAMP(src[0], 0.0f, 4294967295.0f); > + value |= (uint32_t)CLAMP(src[0], 0.0f, 4294967040.0f); > > - value |= (uint32_t)((int32_t)CLAMP(src[0], -2147483648.0f, > 2147483647.0f)); > + value |= (uint32_t)((int32_t)CLAMP(src[0], -2147483648.0f, > 2147483520.0f)); > --- > src/gallium/auxiliary/util/u_format_pack.py | 27 +++ > 1 file changed, 27 insertions(+) > > diff --git a/src/gallium/auxiliary/util/u_format_pack.py > b/src/gallium/auxiliary/util/u_format_pack.py > index 90f348e..d5138cc 100644 > --- a/src/gallium/auxiliary/util/u_format_pack.py > +++ b/src/gallium/auxiliary/util/u_format_pack.py > @@ -207,9 +207,36 @@ def get_one_shift(type): > assert False > > > +def truncate_mantissa(x, bits): > +'''Truncate an integer so it can be represented exactly with a floating > +point mantissa''' > + > +assert isinstance(x, (int, long)) > + > +s = 1 > +if x < 0: > +s = -1 > +x = -x > + > +# We can represent integers up to mantissa + 1 bits exactly > +mask = (1 << (bits + 1)) - 1 > + > +# Slide the mask until the MSB matches > +shift = 0 > +while (x >> shift) & ~mask: > +shift += 1 > + > +x &= mask << shift > +x *= s > +return x > + > + > def value_to_native(type, value): > '''Get the value of unity for this type.''' > if type.type == FLOAT: > +if type.size <= 32 \ > +and isinstance(value, (int, long)): > +return truncate_mantissa(value, 23) > return value > if type.type == FIXED: > return int(value * (1 << (type.size/2))) > ___ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
Re: [Mesa-dev] [PATCH] util/format: Fix clamping to 32bit integers.
> I guess ideally you'd generate code which actually clamps to the max int value representable instead Yes, that would be more complex to generate. Jose From: Roland Scheidegger Sent: 07 November 2014 21:40 To: Jose Fonseca; mesa-dev@lists.freedesktop.org; chr...@ijw.co.nz Subject: Re: [PATCH] util/format: Fix clamping to 32bit integers. Looks good to me though I barely understand the code there... I guess ideally you'd generate code which actually clamps to the max int value representable instead, but that probably would get even more messy (something like: val = MAX(src[0], -2147483648.0f) if (src[0] >= 2147483648.0f) val = 2147483647) Reviewed-by: Roland Scheidegger Am 07.11.2014 um 22:25 schrieb jfons...@vmware.com: > From: José Fonseca > > Use clamping constants that guarantee no integer overflows. > > As spotted by Chris Forbes. > > This causes the code to change as: > > - value |= (uint32_t)CLAMP(src[0], 0.0f, 4294967295.0f); > + value |= (uint32_t)CLAMP(src[0], 0.0f, 4294967040.0f); > > - value |= (uint32_t)((int32_t)CLAMP(src[0], -2147483648.0f, > 2147483647.0f)); > + value |= (uint32_t)((int32_t)CLAMP(src[0], -2147483648.0f, > 2147483520.0f)); > --- > src/gallium/auxiliary/util/u_format_pack.py | 27 +++ > 1 file changed, 27 insertions(+) > > diff --git a/src/gallium/auxiliary/util/u_format_pack.py > b/src/gallium/auxiliary/util/u_format_pack.py > index 90f348e..d5138cc 100644 > --- a/src/gallium/auxiliary/util/u_format_pack.py > +++ b/src/gallium/auxiliary/util/u_format_pack.py > @@ -207,9 +207,36 @@ def get_one_shift(type): > assert False > > > +def truncate_mantissa(x, bits): > +'''Truncate an integer so it can be represented exactly with a floating > +point mantissa''' > + > +assert isinstance(x, (int, long)) > + > +s = 1 > +if x < 0: > +s = -1 > +x = -x > + > +# We can represent integers up to mantissa + 1 bits exactly > +mask = (1 << (bits + 1)) - 1 > + > +# Slide the mask until the MSB matches > +shift = 0 > +while (x >> shift) & ~mask: > +shift += 1 > + > +x &= mask << shift > +x *= s > +return x > + > + > def value_to_native(type, value): > '''Get the value of unity for this type.''' > if type.type == FLOAT: > +if type.size <= 32 \ > +and isinstance(value, (int, long)): > +return truncate_mantissa(value, 23) > return value > if type.type == FIXED: > return int(value * (1 << (type.size/2))) > ___ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
