[Mesa-dev] [RFC 02/11] glsl: Add "built-in" function to do neg(fp64)

[tournier.elie]

On 3 March 2017 at 16:29, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Fri, Mar 3, 2017 at 11:22 AM, Elie Tournier <tournier.elie at gmail.com> wrote:
>> Signed-off-by: Elie Tournier <elie.tournier at collabora.com>
>> ---
>>  src/compiler/glsl/builtin_float64.h     | 19 +++++++++++++++++++
>>  src/compiler/glsl/builtin_functions.cpp |  4 ++++
>>  src/compiler/glsl/builtin_functions.h   |  3 +++
>>  src/compiler/glsl/float64.glsl          | 10 ++++++++++
>>  4 files changed, 36 insertions(+)
>>
>> diff --git a/src/compiler/glsl/builtin_float64.h b/src/compiler/glsl/builtin_float64.h
>> index c1ec89d210..6df91e10f5 100644
>> --- a/src/compiler/glsl/builtin_float64.h
>> +++ b/src/compiler/glsl/builtin_float64.h
>> @@ -17,3 +17,22 @@ fabs64(void *mem_ctx, builtin_available_predicate avail)
>>     sig->replace_parameters(&sig_parameters);
>>     return sig;
>>  }
>> +ir_function_signature *
>> +fneg64(void *mem_ctx, builtin_available_predicate avail)
>> +{
>> +   ir_function_signature *const sig =
>> +      new(mem_ctx) ir_function_signature(glsl_type::uvec2_type, avail);
>> +   ir_factory body(&sig->body, mem_ctx);
>> +   sig->is_defined = true;
>> +
>> +   exec_list sig_parameters;
>> +
>> +   ir_variable *const r000C = new(mem_ctx) ir_variable(glsl_type::uvec2_type, "a", ir_var_function_in);
>> +   sig_parameters.push_tail(r000C);
>> +   body.emit(assign(r000C, bit_xor(swizzle_x(r000C), body.constant(2147483648u)), 0x01));
>> +
>> +   body.emit(ret(r000C));
>> +
>> +   sig->replace_parameters(&sig_parameters);
>> +   return sig;
>> +}
>> diff --git a/src/compiler/glsl/builtin_functions.cpp b/src/compiler/glsl/builtin_functions.cpp
>> index b0b1781725..a189b84190 100644
>> --- a/src/compiler/glsl/builtin_functions.cpp
>> +++ b/src/compiler/glsl/builtin_functions.cpp
>> @@ -3133,6 +3133,10 @@ builtin_builder::create_builtins()
>>                  generate_ir::fabs64(mem_ctx, integer_functions_supported),
>>                  NULL);
>>
>> +   add_function("__builtin_fneg64",
>> +                generate_ir::fneg64(mem_ctx, integer_functions_supported),
>> +                NULL);
>> +
>>  #undef F
>>  #undef FI
>>  #undef FIUD_VEC
>> diff --git a/src/compiler/glsl/builtin_functions.h b/src/compiler/glsl/builtin_functions.h
>> index abe02d97b6..37c6cc33c2 100644
>> --- a/src/compiler/glsl/builtin_functions.h
>> +++ b/src/compiler/glsl/builtin_functions.h
>> @@ -66,6 +66,9 @@ sign64(void *mem_ctx, builtin_available_predicate avail);
>>  ir_function_signature *
>>  fabs64(void *mem_ctx, builtin_available_predicate avail);
>>
>> +ir_function_signature *
>> +fneg64(void *mem_ctx, builtin_available_predicate avail);
>> +
>>  }
>>
>>  #endif /* BULITIN_FUNCTIONS_H */
>> diff --git a/src/compiler/glsl/float64.glsl b/src/compiler/glsl/float64.glsl
>> index b8f0c2e444..82875e9407 100644
>> --- a/src/compiler/glsl/float64.glsl
>> +++ b/src/compiler/glsl/float64.glsl
>> @@ -26,3 +26,13 @@ fabs64( uvec2 a )
>>      a.x &= 0x7FFFFFFFu;
>>      return a;
>>  }
>> +
>> +/* Negate value of a Float64 :
>> + * Toggle the sign bit
>> + */
>> +uvec2
>> +fneg64( uvec2 a )
>> +{
>> +    a.x ^= (1u<<31);
>
> Is this right for NaN? Presumably neg(NaN) should == NaN.

The IEEE 754 standard say :

" 6.3 The sign bit

When either an input or result is NaN, this standard does not
interpret the sign of a NaN. Note, however,
that operations on bit strings copy, negate, abs, copySign specify the
sign bit of a NaN result,
sometimes based upon the sign bit of a NaN operand. The logical
predicate totalOrder is also affected by
the sign bit of a NaN operand. For all other operations, this standard
does not specify the sign bit of a NaN
result, even when there is only one input NaN, or when the NaN is
produced from an invalid operation. "

So neg(NaN) == NaN

>
>> +    return a;
>> +}
>> --
>> 2.11.0
>>
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