// Copyright (c) 2015-2018 Khronos Group. This work is licensed under a // Creative Commons Attribution 4.0 International License; see // http://creativecommons.org/licenses/by/4.0/ [appendix] [[spirvenv]] = Vulkan Environment for SPIR-V Shaders for Vulkan are defined by the <> as well as the <> Specification. This appendix defines additional SPIR-V requirements applying to Vulkan shaders. == Versions and Formats ifdef::VK_VERSION_1_1[] A Vulkan 1.1 implementation must: support the 1.0, 1.1, 1.2, and 1.3 versions of SPIR-V and the 1.0 version of the SPIR-V Extended Instructions for GLSL. endif::VK_VERSION_1_1[] ifndef::VK_VERSION_1_1[] A Vulkan 1.0 implementation must: support the 1.0 version of SPIR-V and the 1.0 version of the SPIR-V Extended Instructions for GLSL. endif::VK_VERSION_1_1[] A SPIR-V module passed into flink:vkCreateShaderModule is interpreted as a series of 32-bit words in host endianness, with literal strings packed as described in section 2.2 of the SPIR-V Specification. The first few words of the SPIR-V module must: be a magic number and a SPIR-V version number, as described in section 2.3 of the SPIR-V Specification. [[spirvenv-capabilities]] == Capabilities The SPIR-V capabilities listed below must: be supported if the corresponding feature or extension is enabled, or if no features or extensions are listed for that capability. Extensions are only listed when there is not also a feature bit associated with that capability. [[spirvenv-capabilities-table]] .List of SPIR-V Capabilities and enabling features or extensions [options="header"] |==== | SPIR-V code:OpCapability | Vulkan feature or extension name | code:Matrix | | code:Shader | | code:InputAttachment | | code:Sampled1D | | code:Image1D | | code:SampledBuffer | | code:ImageBuffer | | code:ImageQuery | | code:DerivativeControl | | code:Geometry | <> | code:Tessellation | <> | code:Float64 | <> | code:Int64 | <> | code:Int16 | <> | code:TessellationPointSize | <> | code:GeometryPointSize | <> | code:ImageGatherExtended | <> | code:StorageImageMultisample | <> | code:UniformBufferArrayDynamicIndexing | <> | code:SampledImageArrayDynamicIndexing | <> | code:StorageBufferArrayDynamicIndexing | <> | code:StorageImageArrayDynamicIndexing | <> | code:ClipDistance | <> | code:CullDistance | <> | code:ImageCubeArray | <> | code:SampleRateShading | <> | code:SparseResidency | <> | code:MinLod | <> | code:SampledCubeArray | <> | code:ImageMSArray | <> | code:StorageImageExtendedFormats | <> | code:InterpolationFunction | <> | code:StorageImageReadWithoutFormat | <> | code:StorageImageWriteWithoutFormat | <> | code:MultiViewport | <> ifdef::VK_VERSION_1_1,VK_KHR_shader_draw_parameters[] | code:DrawParameters | ifdef::VK_VERSION_1_1[] <> endif::VK_VERSION_1_1[] ifdef::VK_KHR_shader_draw_parameters+VK_VERSION_1_1[] or endif::VK_KHR_shader_draw_parameters+VK_VERSION_1_1[] ifdef::VK_KHR_shader_draw_parameters[] <> endif::VK_KHR_shader_draw_parameters[] endif::VK_VERSION_1_1,VK_KHR_shader_draw_parameters[] ifdef::VK_VERSION_1_1,VK_KHR_multiview[] [[spirvenv-capabilities-multiview]] | code:MultiView | ifndef::VK_VERSION_1_1[] <> endif::VK_VERSION_1_1[] endif::VK_VERSION_1_1,VK_KHR_multiview[] ifdef::VK_VERSION_1_1,VK_KHR_device_group[] | code:DeviceGroup | ifndef::VK_VERSION_1_1[] <> endif::VK_VERSION_1_1[] endif::VK_VERSION_1_1,VK_KHR_device_group[] ifdef::VK_VERSION_1_1,VK_KHR_variable_pointers[] [[spirvenv-capabilities-table-variablepointers]] | code:VariablePointersStorageBuffer | <> | code:VariablePointers | <> endif::VK_VERSION_1_1,VK_KHR_variable_pointers[] ifdef::VK_EXT_shader_stencil_export[] [[spirvenv-capabilities-table-shaderstencilexportext]] | code:StencilExportEXT | `<>` endif::VK_EXT_shader_stencil_export[] ifdef::VK_EXT_shader_subgroup_ballot[] [[spirvenv-capabilities-table-subgroupballot]] | code:SubgroupBallotKHR | `<>` endif::VK_EXT_shader_subgroup_ballot[] ifdef::VK_EXT_shader_subgroup_vote[] [[spirvenv-capabilities-table-subgroupvote]] | code:SubgroupVoteKHR | `<>` endif::VK_EXT_shader_subgroup_vote[] ifdef::VK_AMD_shader_image_load_store_lod[] [[spirvenv-capabilities-table-imagereadwritelodamd]] | code:ImageReadWriteLodAMD | `<>` endif::VK_AMD_shader_image_load_store_lod[] ifdef::VK_AMD_texture_gather_bias_lod[] [[spirvenv-capabilities-table-imagegatherbiaslodamd]] | code:ImageGatherBiasLodAMD | `<>` endif::VK_AMD_texture_gather_bias_lod[] ifdef::VK_AMD_shader_fragment_mask[] [[spirvenv-capabilities-table-fragmentmaskamd]] | code:FragmentMaskAMD | `<>` endif::VK_AMD_shader_fragment_mask[] ifdef::VK_NV_sample_mask_override_coverage[] [[spirvenv-capabilities-table-samplemaskoverridecoverage]] | code:SampleMaskOverrideCoverageNV | `<>` endif::VK_NV_sample_mask_override_coverage[] ifdef::VK_NV_geometry_shader_passthrough[] [[spirvenv-capabilities-table-geometryshaderpassthrough]] | code:GeometryShaderPassthroughNV | `<>` endif::VK_NV_geometry_shader_passthrough[] ifdef::VK_EXT_shader_viewport_index_layer[] [[spirvenv-capabilities-table-shader-viewport-index-layer]] | code:ShaderViewportIndexLayerEXT | `<>` endif::VK_EXT_shader_viewport_index_layer[] ifdef::VK_NV_viewport_array2[] [[spirvenv-capabilities-table-viewportarray2]] | code:ShaderViewportIndexLayerNV | `<>` | code:ShaderViewportMaskNV | `<>` endif::VK_NV_viewport_array2[] ifdef::VK_NVX_multiview_per_view_attributes[] [[spirvenv-capabilities-table-perviewattributes]] | code:PerViewAttributesNV | `<>` endif::VK_NVX_multiview_per_view_attributes[] ifdef::VK_VERSION_1_1,VK_KHR_16bit_storage[] [[spirvenv-capabilities-table-16bitstorage]] | code:StorageBuffer16BitAccess | <> | code:UniformAndStorageBuffer16BitAccess | <> | code:StoragePushConstant16 | <> | code:StorageInputOutput16 | <> endif::VK_VERSION_1_1,VK_KHR_16bit_storage[] ifdef::VK_VERSION_1_1[] [[spirvenv-capabilities-table-subgroup]] | code:GroupNonUniform | <> | code:GroupNonUniformVote | <> | code:GroupNonUniformArithmetic | <> | code:GroupNonUniformBallot | <> | code:GroupNonUniformShuffle | <> | code:GroupNonUniformShuffleRelative | <> | code:GroupNonUniformClustered | <> | code:GroupNonUniformQuad | <> ifdef::VK_NV_shader_subgroup_partitioned[] | code:GroupNonUniformPartitionedNV | <> endif::VK_NV_shader_subgroup_partitioned[] endif::VK_VERSION_1_1[] ifdef::VK_EXT_post_depth_coverage[] [[spirvenv-capabilities-table-postdepthcoverage]] | code:SampleMaskPostDepthCoverage | `<>` endif::VK_EXT_post_depth_coverage[] ifdef::VK_EXT_descriptor_indexing[] [[spirvenv-capabilities-table-descriptorindexing]] | code:ShaderNonUniformEXT | `<>` | code:RuntimeDescriptorArrayEXT | <> | code:InputAttachmentArrayDynamicIndexingEXT | <> | code:UniformTexelBufferArrayDynamicIndexingEXT | <> | code:StorageTexelBufferArrayDynamicIndexingEXT | <> | code:UniformBufferArrayNonUniformIndexingEXT | <> | code:SampledImageArrayNonUniformIndexingEXT | <> | code:StorageBufferArrayNonUniformIndexingEXT | <> | code:StorageImageArrayNonUniformIndexingEXT | <> | code:InputAttachmentArrayNonUniformIndexingEXT | <> | code:UniformTexelBufferArrayNonUniformIndexingEXT | <> | code:StorageTexelBufferArrayNonUniformIndexingEXT | <> endif::VK_EXT_descriptor_indexing[] ifdef::VK_AMD_gpu_shader_half_float[] | code:Float16 | `<>` endif::VK_AMD_gpu_shader_half_float[] ifdef::VK_KHR_8bit_storage[] [[spirvenv-capabilities-table-8bitstorage]] | code:StorageBuffer8BitAccess | <> | code:UniformAndStorageBuffer8BitAccess | <> | code:StoragePushConstant8 | <> endif::VK_KHR_8bit_storage[] |==== ifdef::VK_VERSION_1_1,VK_KHR_variable_pointers[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_KHR_variable_pointers` SPIR-V extension. endif::VK_VERSION_1_1,VK_KHR_variable_pointers[] ifdef::VK_AMD_shader_explicit_vertex_parameter[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_AMD_shader_explicit_vertex_parameter` SPIR-V extension. endif::VK_AMD_shader_explicit_vertex_parameter[] ifdef::VK_AMD_gcn_shader[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_AMD_gcn_shader` SPIR-V extension. endif::VK_AMD_gcn_shader[] ifdef::VK_AMD_gpu_shader_half_float[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_AMD_gpu_shader_half_float` SPIR-V extension. endif::VK_AMD_gpu_shader_half_float[] ifdef::VK_AMD_gpu_shader_int16[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_AMD_gpu_shader_int16` SPIR-V extension. endif::VK_AMD_gpu_shader_int16[] ifdef::VK_AMD_shader_ballot[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_AMD_shader_ballot` SPIR-V extension. endif::VK_AMD_shader_ballot[] ifdef::VK_AMD_shader_fragment_mask[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_AMD_shader_fragment_mask` SPIR-V extension. endif::VK_AMD_shader_fragment_mask[] ifdef::VK_AMD_shader_image_load_store_lod[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_AMD_shader_image_load_store_lod` SPIR-V extension. endif::VK_AMD_shader_image_load_store_lod[] ifdef::VK_AMD_shader_trinary_minmax[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_AMD_shader_trinary_minmax` SPIR-V extension. endif::VK_AMD_shader_trinary_minmax[] ifdef::VK_AMD_texture_gather_bias_lod[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_AMD_texture_gather_bias_lod` SPIR-V extension. endif::VK_AMD_texture_gather_bias_lod[] ifdef::VK_VERSION_1_1,VK_KHR_shader_draw_parameters[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_KHR_shader_draw_parameters` SPIR-V extension. endif::VK_VERSION_1_1,VK_KHR_shader_draw_parameters[] ifdef::VK_KHR_8bit_storage[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the +SPV_KHR_8bit_storage+ SPIR-V extension. endif::VK_KHR_8bit_storage[] ifdef::VK_VERSION_1_1,VK_KHR_16bit_storage[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the https://www.khronos.org/registry/spir-v/extensions/KHR/SPV_KHR_16bit_storage.html[`SPV_KHR_16bit_storage`] SPIR-V extension. endif::VK_VERSION_1_1,VK_KHR_16bit_storage[] ifdef::VK_VERSION_1_1,VK_KHR_storage_buffer_storage_class[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the https://www.khronos.org/registry/spir-v/extensions/KHR/SPV_KHR_storage_buffer_storage_class.html[`SPV_KHR_storage_buffer_storage_class`] SPIR-V extension. endif::VK_VERSION_1_1,VK_KHR_storage_buffer_storage_class[] ifdef::VK_EXT_post_depth_coverage[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_KHR_post_depth_coverage` SPIR-V extension. endif::VK_EXT_post_depth_coverage[] ifdef::VK_EXT_shader_stencil_export[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_EXT_shader_stencil_export` SPIR-V extension. endif::VK_EXT_shader_stencil_export[] ifdef::VK_EXT_shader_subgroup_ballot[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_KHR_shader_ballot` SPIR-V extension. endif::VK_EXT_shader_subgroup_ballot[] ifdef::VK_EXT_shader_subgroup_vote[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_KHR_subgroup_vote` SPIR-V extension. endif::VK_EXT_shader_subgroup_vote[] ifdef::VK_NV_sample_mask_override_coverage[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_NV_sample_mask_override_coverage` SPIR-V extension. endif::VK_NV_sample_mask_override_coverage[] ifdef::VK_NV_geometry_shader_passthrough[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_NV_geometry_shader_passthrough` SPIR-V extension. endif::VK_NV_geometry_shader_passthrough[] ifdef::VK_NV_viewport_array2[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_NV_viewport_array2` SPIR-V extension. endif::VK_NV_viewport_array2[] ifdef::VK_EXT_shader_viewport_index_layer[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_EXT_shader_viewport_index_layer` SPIR-V extension. endif::VK_EXT_shader_viewport_index_layer[] ifdef::VK_NVX_multiview_per_view_attributes[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the `SPV_NVX_multiview_per_view_attributes` SPIR-V extension. endif::VK_NVX_multiview_per_view_attributes[] ifdef::VK_EXT_descriptor_indexing[] The application can: pass a SPIR-V module to flink:vkCreateShaderModule that uses the +SPV_EXT_descriptor_indexing+ SPIR-V extension. endif::VK_EXT_descriptor_indexing[] The application must: not pass a SPIR-V module containing any of the following to flink:vkCreateShaderModule: * any OpCapability not listed above, * an unsupported capability, or * a capability which corresponds to a Vulkan feature or extension which has not been enabled. [[spirvenv-module-validation]] == Validation Rules within a Module A SPIR-V module passed to flink:vkCreateShaderModule must: conform to the following rules: * Every entry point must: have no return value and accept no arguments. * Recursion: The static function-call graph for an entry point must: not contain cycles. * The *Logical* addressing model must: be selected. * *Scope* for execution must: be limited to: ** *Workgroup* ** *Subgroup* * *Scope* for memory must: be limited to: ** *Device* ** *Workgroup* ifdef::VK_VERSION_1_1[] ** *Subgroup* endif::VK_VERSION_1_1[] ** *Invocation* ifdef::VK_VERSION_1_1[] * *Scope* for *Non Uniform Group Operations* must: be limited to: ** *Subgroup* endif::VK_VERSION_1_1[] * *Storage Class* must: be limited to: ** *UniformConstant* ** *Input* ** *Uniform* ** *Output* ** *Workgroup* ** *Private* ** *Function* ** *PushConstant* ** *Image* ifdef::VK_VERSION_1_1,VK_KHR_storage_buffer_storage_class[] ** *StorageBuffer* endif::VK_VERSION_1_1,VK_KHR_storage_buffer_storage_class[] * Memory semantics must: obey the following rules: ** *Acquire* must: not be used with code:OpAtomicStore. ** *Release* must: not be used with code:OpAtomicLoad. ** *AcquireRelease* must: not be used with code:OpAtomicStore or code:OpAtomicLoad. ** Sequentially consistent atomics and barriers are not supported and *SequentiallyConsistent* is treated as *AcquireRelease*. *SequentiallyConsistent* should: not be used. ** code:OpMemoryBarrier must: use one of *Acquire*, *Release*, *AcquireRelease*, or *SequentiallyConsistent* and must: include at least one storage class. ** If the semantics for code:OpControlBarrier includes one of *Acquire*, *Release*, *AcquireRelease*, or *SequentiallyConsistent*, then it must: include at least one storage class. ** *SubgroupMemory*, *CrossWorkgroupMemory*, and *AtomicCounterMemory* are ignored. * Any code:OpVariable with an code:Initializer operand must: have one of the following as its code:Storage code:Class operand: ** *Output* ** *Private* ** *Function* * The code:OriginLowerLeft execution mode must: not be used; fragment entry points must: declare code:OriginUpperLeft. * The code:PixelCenterInteger execution mode must: not be used. Pixels are always centered at half-integer coordinates. * Images and Samplers ** code:OpTypeImage must: declare a scalar 32-bit float or 32-bit integer type for the "`Sampled Type`". (code:RelaxedPrecision can: be applied to a sampling instruction and to the variable holding the result of a sampling instruction.) ** code:OpTypeImage must: have a "`Sampled`" operand of 1 (sampled image) or 2 (storage image). ** If <> is not enabled and an code:OpTypeImage has "`Image Format`" operand of code:Unknown, any variables created with the given type must be decorated with code:NonReadable. ** If <> is not enabled and an code:OpTypeImage has "`Image Format`" operand of code:Unknown, any variables created with the given type must be decorated with code:NonWritable. ** code:OpImageQuerySizeLod, and code:OpImageQueryLevels must: only consume an "`Image`" operand whose type has its "`Sampled`" operand set to 1. ** The [eq]#(u,v)# coordinates used for a code:SubpassData must: be the of a constant vector [eq]#(0,0)#, or if a layer coordinate is used, must: be a vector that was formed with constant 0 for the [eq]#u# and [eq]#v# components. ** The "`Depth`" operand of code:OpTypeImage is ignored. ** Objects of types code:OpTypeImage, code:OpTypeSampler, code:OpTypeSampledImage, and arrays of these types must: not be stored to or modified. * Decorations ** The code:GLSLShared and code:GLSLPacked decorations must: not be used. ** The code:Flat, code:NoPerspective, code:Sample, and code:Centroid decorations must: not be used on variables with storage class other than code:Input or on variables used in the interface of non-fragment shader entry points. ** The code:Patch decoration must: not be used on variables in the interface of a vertex, geometry, or fragment shader stage's entry point. ifdef::VK_NV_viewport_array2[] ** The code:ViewportRelativeNV decoration must: only be used on a variable decorated with code:Layer in the vertex, tessellation evaluation, or geometry shader stages. ** The code:ViewportRelativeNV decoration must: not be used unless a variable decorated with one of code:ViewportIndex or code:ViewportMaskNV is also statically used by the same code:OpEntryPoint. ** The code:ViewportMaskNV and code:ViewportIndex decorations must: not both be statically used by one or more code:OpEntryPoint's that form the vertex processing stages of a graphics pipeline. endif::VK_NV_viewport_array2[] ifdef::VK_VERSION_1_1,VK_KHR_16bit_storage[] ** Only the round-to-nearest-even and the round-to-zero rounding modes can: be used for the code:FPRoundingMode decoration. ** The code:FPRoundingMode decoration can: only be used for the floating-point conversion instructions as described in the https://www.khronos.org/registry/spir-v/extensions/KHR/SPV_KHR_16bit_storage.html[`SPV_KHR_16bit_storage`] SPIR-V extension. endif::VK_VERSION_1_1,VK_KHR_16bit_storage[] ** code:DescriptorSet and code:Binding decorations must: obey the constraints on storage class, type, and descriptor type described in <> * code:OpTypeRuntimeArray must: only be used for: ** the last member of an code:OpTypeStruct ifdef::VK_VERSION_1_1,VK_KHR_storage_buffer_storage_class[] that is in the code:StorageBuffer storage class decorated as code:Block, or endif::VK_VERSION_1_1,VK_KHR_storage_buffer_storage_class[] that is in the code:Uniform storage class decorated as code:BufferBlock. ifdef::VK_EXT_descriptor_indexing[] ** If the code:RuntimeDescriptorArrayEXT capability is supported, an array of variables with storage class code:Uniform, ifdef::VK_VERSION_1_1,VK_KHR_storage_buffer_storage_class[] code:StorageBuffer, endif::VK_VERSION_1_1,VK_KHR_storage_buffer_storage_class[] or code:UniformConstant, or for the outermost dimension of an array of arrays of such variables. endif::VK_EXT_descriptor_indexing[] * Linkage: See <> for additional linking and validation rules. ifdef::VK_VERSION_1_1[] * If code:OpControlBarrier is used in fragment, vertex, tessellation evaluation, or geometry stages, the execution Scope must: be code:Subgroup. endif::VK_VERSION_1_1[] * Compute Shaders ** For each compute shader entry point, either a code:LocalSize execution mode or an object decorated with the code:WorkgroupSize decoration must: be specified. ifdef::VK_VERSION_1_1[] * "`Result Type`" for *Non Uniform Group Operations* must: be limited to 32-bit float, 32-bit integer, boolean, or vectors of these types. If the code:Float64 capability is enabled, double and vector of double types are also permitted. * "`Mask`" for code:OpGroupNonUniformShuffleXor must: be a specialization constant or a constant, or if the dynamic instance is called within a loop construct it must: be one of: . A specialization constant. . A constant. . An arthimetic operation whose operands are 1., 2., or 4. . A phi node whose operands are 1., 2., or 3. * If code:OpGroupNonUniformBallotBitCount is used, the group operation must: be one of: ** *Reduce* ** *InclusiveScan* ** *ExclusiveScan* endif::VK_VERSION_1_1[] * Atomic instructions must: declare a scalar 32-bit integer type for the _Result Type_ and the type of the value pointed to by _Pointer_. ifdef::VK_EXT_descriptor_indexing[] * If an instruction loads from or stores to a resource (including atomics and image instructions) and the resource descriptor being accessed is not dynamically uniform, then the operand corresponding to that resource (e.g. the pointer or sampled image operand) must: be decorated with code:NonUniformEXT. endif::VK_EXT_descriptor_indexing[] [[spirvenv-precision-operation]] == Precision and Operation of SPIR-V Instructions The following rules apply to both single and double-precision floating point instructions: * Positive and negative infinities and positive and negative zeros are generated as dictated by <>, but subject to the precisions allowed in the following table. * Dividing a non-zero by a zero results in the appropriately signed <> infinity. * Any denormalized value input into a shader or potentially generated by any instruction in a shader may: be flushed to 0. * The rounding mode cannot: be set and is undefined. * [eq]##NaN##s may: not be generated. Instructions that operate on a [eq]#NaN# may: not result in a [eq]#NaN#. * Support for signaling [eq]##NaN##s is optional: and exceptions are never raised. The precision of double-precision instructions is at least that of single precision. The precision of operations is defined either in terms of rounding, as an error bound in ULP, or as inherited from a formula as follows. .Correctly Rounded Operations described as "correctly rounded" will return the infinitely precise result, [eq]#x#, rounded so as to be representable in floating-point. The rounding mode used is not defined but if [eq]#x# is exactly representable then [eq]#x# will be returned. Otherwise, either the floating-point value closest to and no less than [eq]#x# or the value closest to and no greater than [eq]#x# will be returned. .ULP Where an error bound of [eq]#n# ULP (units in the last place) is given, for an operation with infinitely precise result #x# the value returned must be in the range #[x - n * ulp(x), x + n * ulp(x)]#. The function #ulp(x)# is defined as follows: :: If there exist non-equal floating-point numbers #a# and #b# such that [eq]#a {leq} x {leq} b# then #ulp(x)# is the minimum possible distance between such numbers, latexmath:[ulp(x) = \mathrm{min}_{a,b} | b - a |]. If such numbers do not exist then #ulp(x)# is defined to be the difference between the two finite floating-point numbers nearest to #x#. Where the range of allowed return values includes any value of magnitude larger than that of the largest representable finite floating-point number, operations may return an infinity of the appropriate sign. If the infinitely precise result of the operation is not mathematically defined then the value returned is undefined. .Inherited From ... Where an operation's precision is described as being inherited from a formula, the result returned must be at least as accurate as the result of computing an approximation to [eq]#x# using a formula equivalent to the given formula applied to the supplied inputs. Specifically, the formula given may be transformed using the mathematical associativity, commutativity and distributivity of the operators involved to yield an equivalent formula. The SPIR-V precision rules, when applied to each such formula and the given input values, define a range of permitted values. If [eq]#NaN# is one of the permitted values then the operation may return any result, otherwise let the largest permitted value in any of the ranges be [eq]#F~max~# and the smallest be [eq]#F~min~#. The operation must return a value in the range [eq]#[x - E, x + E]# where latexmath:[E = \mathrm{max} \left( | x - F_{\mathrm{min}} |, | x - F_{\mathrm{max}} | \right) ] For single precision (32 bit) instructions, precisions are required: to be at least as follows, unless decorated with RelaxedPrecision: .Precision of core SPIR-V Instructions [options="header"] |==== | Instruction | Precision | code:OpFAdd | Correctly rounded. | code:OpFSub | Correctly rounded. | code:OpFMul | Correctly rounded. | code:OpFOrdEqual, code:OpFUnordEqual | Correct result. | code:OpFOrdLessThan, code:OpFUnordLessThan | Correct result. | code:OpFOrdGreaterThan, code:OpFUnordGreaterThan | Correct result. | code:OpFOrdLessThanEqual, code:OpFUnordLessThanEqual | Correct result. | code:OpFOrdGreaterThanEqual, code:OpFUnordGreaterThanEqual| Correct result. | code:OpFDiv | 2.5 ULP for b in the range [2^-126^, 2^126^]. | conversions between types | Correctly rounded. |==== .Precision of GLSL.std.450 Instructions [options="header"] |==== |Instruction | Precision | code:fma() | Inherited from code:OpFMul followed by code:OpFAdd. | code:exp(x), code:exp2(x) | [eq]#3 {plus} 2 {times} {vert}x{vert}# ULP. | code:log(), code:log2() | 3 ULP outside the range [eq]#[0.5, 2.0]#. Absolute error < [eq]#2^-21^# inside the range [eq]#[0.5, 2.0]#. | code:pow(x, y) | Inherited from code:exp2(y {times} code:log2(x)). | code:sqrt() | Inherited from 1.0 / code:inversesqrt(). | code:inversesqrt() | 2 ULP. |==== GLSL.std.450 extended instructions specifically defined in terms of the above instructions inherit the above errors. GLSL.std.450 extended instructions not listed above and not defined in terms of the above have undefined precision. These include, for example, the trigonometric functions and determinant. For the code:OpSRem and code:OpSMod instructions, if either operand is negative the result is undefined. [NOTE] .Note ==== While the code:OpSRem and code:OpSMod instructions are supported by the Vulkan environment, they require non-negative values and thus do not enable additional functionality beyond what code:OpUMod provides. ==== [[spirvenv-image-formats]] == Compatibility Between SPIR-V Image Formats And Vulkan Formats Images which are read from or written to by shaders must: have SPIR-V image formats compatible with the Vulkan image formats backing the image under the circumstances described for <>. The compatibile formats are: .SPIR-V and Vulkan Image Format Compatibility [cols="2*", options="header"] |==== |SPIR-V Image Format |Compatible Vulkan Format |code:Rgba32f |ename:VK_FORMAT_R32G32B32A32_SFLOAT |code:Rgba16f |ename:VK_FORMAT_R16G16B16A16_SFLOAT |code:R32f |ename:VK_FORMAT_R32_SFLOAT |code:Rgba8 |ename:VK_FORMAT_R8G8B8A8_UNORM |code:Rgba8Snorm |ename:VK_FORMAT_R8G8B8A8_SNORM |code:Rg32f |ename:VK_FORMAT_R32G32_SFLOAT |code:Rg16f |ename:VK_FORMAT_R16G16_SFLOAT |code:R11fG11fB10f |ename:VK_FORMAT_B10G11R11_UFLOAT_PACK32 |code:R16f |ename:VK_FORMAT_R16_SFLOAT |code:Rgba16 |ename:VK_FORMAT_R16G16B16A16_UNORM |code:Rgb10A2 |ename:VK_FORMAT_A2B10G10R10_UNORM_PACK32 |code:Rg16 |ename:VK_FORMAT_R16G16_UNORM |code:Rg8 |ename:VK_FORMAT_R8G8_UNORM |code:R16 |ename:VK_FORMAT_R16_UNORM |code:R8 |ename:VK_FORMAT_R8_UNORM |code:Rgba16Snorm |ename:VK_FORMAT_R16G16B16A16_SNORM |code:Rg16Snorm |ename:VK_FORMAT_R16G16_SNORM |code:Rg8Snorm |ename:VK_FORMAT_R8G8_SNORM |code:R16Snorm |ename:VK_FORMAT_R16_SNORM |code:R8Snorm |ename:VK_FORMAT_R8_SNORM |code:Rgba32i |ename:VK_FORMAT_R32G32B32A32_SINT |code:Rgba16i |ename:VK_FORMAT_R16G16B16A16_SINT |code:Rgba8i |ename:VK_FORMAT_R8G8B8A8_SINT |code:R32i |ename:VK_FORMAT_R32_SINT |code:Rg32i |ename:VK_FORMAT_R32G32_SINT |code:Rg16i |ename:VK_FORMAT_R16G16_SINT |code:Rg8i |ename:VK_FORMAT_R8G8_SINT |code:R16i |ename:VK_FORMAT_R16_SINT |code:R8i |ename:VK_FORMAT_R8_SINT |code:Rgba32ui |ename:VK_FORMAT_R32G32B32A32_UINT |code:Rgba16ui |ename:VK_FORMAT_R16G16B16A16_UINT |code:Rgba8ui |ename:VK_FORMAT_R8G8B8A8_UINT |code:R32ui |ename:VK_FORMAT_R32_UINT |code:Rgb10a2ui |ename:VK_FORMAT_A2B10G10R10_UINT_PACK32 |code:Rg32ui |ename:VK_FORMAT_R32G32_UINT |code:Rg16ui |ename:VK_FORMAT_R16G16_UINT |code:Rg8ui |ename:VK_FORMAT_R8G8_UINT |code:R16ui |ename:VK_FORMAT_R16_UINT |code:R8ui |ename:VK_FORMAT_R8_UINT |====