Name NV_shader_atomic_float64 Name Strings GL_NV_shader_atomic_float64 Contact Kedarnath Thangudu, NVIDIA Corporation (kthangudu 'at' nvidia.com) Contributors Pat Brown, NVIDIA Status Shipping in NVIDIA release 367.XX drivers and up. Version Last Modified Date: October 15, 2014 NVIDIA Revision: 1 Number OpenGL Extension #488 Dependencies This extension is written against the OpenGL 4.5 (Compatibility Profile) Specification. This extension is written against version 4.50 (revision 3) of the OpenGL Shading Language Specification. This extension requires ARB_gpu_shader_fp64 or NV_gpu_program_fp64. This extension interacts with NV_shader_buffer_store, NV_gpu_shader5, ARB_shader_storage_buffer_object, and ARB_compute_shader. This extension interacts with NV_gpu_program5. Overview This extension provides GLSL built-in functions and assembly opcodes allowing shaders to perform atomic read-modify-write operations to buffer or shared memory with double-precision floating-point components. The set of atomic operations provided by this extension is limited to adds and exchanges. Providing atomic add support allows shaders to atomically accumulate the sum of double-precision floating-point values into buffer memory across multiple (possibly concurrent) shader invocations. This extension provides GLSL support for atomics targeting double-precision floating-point pointers (if NV_gpu_shader5 is supported). Additionally, assembly opcodes for these operations are also provided if NV_gpu_program5 is supported. New Procedures and Functions None. New Tokens None. Additions to the OpenGL 4.5 (Compatibility Profile) Specification None. Additions to the AGL/GLX/WGL Specifications None. GLX Protocol None. Modifications to the OpenGL Shading Language Specification, Version 4.50 (revision 3) Including the following line in a shader can be used to control the language features described in this extension: #extension GL_NV_shader_atomic_float64 : where is as specified in section 3.3. New preprocessor #defines are added to the OpenGL Shading Language: #define GL_NV_shader_atomic_float64 1 Modify Section 8.11, Atomic Memory Functions (p. 172) (add to "atomicAdd" table cell, p. 173) double atomicAdd(coherent inout double mem, double data) (add to "atomicExchange" table cell, p. 173) double atomicExchange(coherent inout double mem, double data) Dependencies on NV_shader_buffer_store, NV_gpu_shader5, ARB_shader_storage_buffer_object, and ARB_compute_shader If NV_shader_buffer_store and NV_gpu_shader5 are supported, the following functions should be added to the "Section 8.Y, Shader Memory Functions" language in the NV_shader_buffer_store specification: double atomicAdd(double *address, double data); double atomicExchange(double *address, double data); If ARB_shader_storage_buffer_object or ARB_compute_shader are supported, make similar edits to the functions documented in the ARB_shader_storage_buffer object extension. These functions are available if and only if GL_NV_shader_atomic_float64 is enabled via the "#extension" directive. Dependencies on NV_gpu_program5 If NV_gpu_program5 is supported and "OPTION NV_shader_atomic_float64" is specified in an assembly program, "F64" should be allowed as a storage modifier to the ATOM instruction for the atomic operations "ADD" and "EXCH". (Add to "Section 2.X.6, Program Options" of the NV_gpu_program4 extension, as extended by NV_gpu_program5:) + Double-precision Floating-Point Atomic Operations (NV_shader_atomic_float64) If a program specifies the "NV_shader_atomic_float64" option, it may use "F64" storage modifier with the "ATOM" opcode to perform atomic double- precision floating-point add or exchange operations. (Add to the table in "Section 2.X.8.Z, ATOM" in NV_gpu_program5:) atomic storage modifier modifiers operation -------- ----------------------- --------------------------------- ADD U32, S32, U64, F32, F64 compute a sum F16X2, F16X4 ... EXCH U32, S32, U64, F32, F64 exchange memory with operand F16X2, F16X4 Note: Storage modifier U64 is provided by NV_shader_atomic_int64 Storage modifier F32 is provided by NV_shader_atomic_float Storage modifiers F16X2 and F16X4 are provided by NV_shader_atomic_fp16_vector Errors None. New State None. New Implementation Dependent State None. Issues (1) What double-precision floating-point targets are supported for atomic operations? RESOLVED: This extension only supports atomic operations on double- precision floating-point buffer memory. Atomic operation on double- precision texture memory are not supported since OpenGL provides no pixel/texture formats with double-precision components. (2) What atomic operations should we support for double-precision floating-point targets? RESOLVED: Double-precision floating-point atomic addition is the main functionality targeted by this extension. We provide exchanges because the operation needs no special hardware support. We chose not to provide support for bitwise operations (AND/OR/XOR); it's possible to support these by casting a pointer or aliasing an image if required. Minimum, maximum, and compare-and-swap make sense, but the underlying atomic hardware targeted by this extension does not support floating-point comparisons. Revision History Revision 1 - Internal revisions.