// Copyright (c) 2014-2018 Khronos Group. This work is licensed under a
// Creative Commons Attribution 4.0 International License; see
// http://creativecommons.org/licenses/by/4.0/

include::meta/VK_KHR_shader_float_controls.txt[]

*Last Modified Date*::
    2018-09-11
*IP Status*::
    No known IP claims.
*Interactions and External Dependencies*::
  - This extension requires
    https://www.khronos.org/registry/spir-v/extensions/KHR/SPV_KHR_float_controls.html[`SPV_KHR_float_controls`]
*Contributors*::
    - Alexander Galazin, Arm
    - Jan-Harald Fredriksen, Arm
    - Jeff Bolz, NVIDIA
    - Graeme Leese, Broadcom
    - Daniel Rakos, AMD

=== Description

The `VK_KHR_shader_float_controls` extension enables efficient use of
floating-point computations through the ability to query and override the
implementation's default behavior for rounding modes, denormals, signed
zero, and infinity.

=== New Enum Constants

  * Extending elink:VkStructureType:
  ** ename:VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_FLOAT_CONTROLS_PROPERTIES_KHR

=== New Enums

  * None

=== New Structures

  * slink:VkPhysicalDeviceFloatControlsPropertiesKHR

=== New Functions

  * None

=== New SPIR-V Capabilities

  * <<spirvenv-capabilities-table-shaderfloatcontrols,code:DenormPreserve>>
  * <<spirvenv-capabilities-table-shaderfloatcontrols,code:DenormFlushToZero>>
  * <<spirvenv-capabilities-table-shaderfloatcontrols,code:SignedZeroInfNanPreserve>>
  * <<spirvenv-capabilities-table-shaderfloatcontrols,code:RoundingModeRTE>>
  * <<spirvenv-capabilities-table-shaderfloatcontrols,code:RoundingModeRTZ>>

=== Issues

1) Which instructions must flush denorms?

*RESOLVED*: Only floating-point conversion, floating-point arithmetic,
floating-point relational (except code:OpIsNaN, code:OpIsInf), and
floating-point GLSL.std.450 extended instructions must flush denormals.

2) What is the denorm behavior for intermediate results?

*RESOLVED*: When a SPIR-V instruction is implemented as a sequence of other
instructions:
 - in the code:DenormFlushToZero execution mode the intermediate
   instructions may flush denormals, the final result of the sequence must:
   not be denormal.
 - in the code:DenormPreserve execution mode denormals must be preserved
   throughout the whole sequence.

3) Do denorm and rounding mode controls apply to code:OpSpecConstantOp?

*RESOLVED*: Yes, except when the opcode is code:OpQuantizeToF16.

4) The SPIR-V specification says that code:OpConvertFToU and
code:OpConvertFToS unconditionally round towards zero.
Do the rounding mode controls specified through the execution modes apply to
them?

*RESOLVED*: No, these instructions unconditionally round towards zero.

5) Do any of the "Pack" GLSL.std.450 instructions count as conversion
instructions and have the rounding mode apply?

*RESOLVED*: No, only instructions listed in the section "3.32.11.
Conversion Instructions" of the SPIR-V specification count as conversion
instructions.

6) When using inf/nan-ignore mode, what is expected of code:OpIsNan and
   code:OpIsInf?

*RESOLVED*: These instructions must always accurately detect inf/nan if it
is passed to them.

=== Version History

  * Revision 3, 2018-09-11 (Alexander Galazin)
    - Minor restructuring
  * Revision 2, 2018-04-17 (Alexander Galazin)
    - Added issues and resolutions
  * Revision 1, 2018-04-11 (Alexander Galazin)
    - Initial draft