Appendix A: Vulkan Environment for SPIR-V

Shaders for Vulkan are defined by the Khronos SPIR-V Specification as well as the Khronos SPIR-V Extended Instructions for GLSL Specification. This appendix defines additional SPIR-V requirements applying to Vulkan shaders.

Versions and Formats

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.

A SPIR-V module passed into 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.

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.

Table 65. List of SPIR-V Capabilities and enabling features or extensions
SPIR-V OpCapability Vulkan feature or extension name

Matrix

Shader

InputAttachment

Sampled1D

Image1D

SampledBuffer

ImageBuffer

ImageQuery

DerivativeControl

Geometry

geometryShader

Tessellation

tessellationShader

Float64

shaderFloat64

Int64

shaderInt64

Int64Atomics

VK_KHR_shader_atomic_int64

Int16

shaderInt16

TessellationPointSize

shaderTessellationAndGeometryPointSize

GeometryPointSize

shaderTessellationAndGeometryPointSize

ImageGatherExtended

shaderImageGatherExtended

StorageImageMultisample

shaderStorageImageMultisample

UniformBufferArrayDynamicIndexing

shaderUniformBufferArrayDynamicIndexing

SampledImageArrayDynamicIndexing

shaderSampledImageArrayDynamicIndexing

StorageBufferArrayDynamicIndexing

shaderStorageBufferArrayDynamicIndexing

StorageImageArrayDynamicIndexing

shaderStorageImageArrayDynamicIndexing

ClipDistance

shaderClipDistance

CullDistance

shaderCullDistance

ImageCubeArray

imageCubeArray

SampleRateShading

sampleRateShading

SparseResidency

shaderResourceResidency

MinLod

shaderResourceMinLod

SampledCubeArray

imageCubeArray

ImageMSArray

shaderStorageImageMultisample

StorageImageExtendedFormats

InterpolationFunction

sampleRateShading

StorageImageReadWithoutFormat

shaderStorageImageReadWithoutFormat

StorageImageWriteWithoutFormat

shaderStorageImageWriteWithoutFormat

MultiViewport

multiViewport

DrawParameters

shaderDrawParameters or VK_KHR_shader_draw_parameters

MultiView

DeviceGroup

VariablePointersStorageBuffer

variablePointersStorageBuffer

VariablePointers

variablePointers

StorageBuffer16BitAccess

StorageBuffer16BitAccess

UniformAndStorageBuffer16BitAccess

UniformAndStorageBuffer16BitAccess

StoragePushConstant16

storagePushConstant16

StorageInputOutput16

storageInputOutput16

GroupNonUniform

VK_SUBGROUP_FEATURE_BASIC_BIT

GroupNonUniformVote

VK_SUBGROUP_FEATURE_VOTE_BIT

GroupNonUniformArithmetic

VK_SUBGROUP_FEATURE_ARITHMETIC_BIT

GroupNonUniformBallot

VK_SUBGROUP_FEATURE_BALLOT_BIT

GroupNonUniformShuffle

VK_SUBGROUP_FEATURE_SHUFFLE_BIT

GroupNonUniformShuffleRelative

VK_SUBGROUP_FEATURE_SHUFFLE_RELATIVE_BIT

GroupNonUniformClustered

VK_SUBGROUP_FEATURE_CLUSTERED_BIT

GroupNonUniformQuad

VK_SUBGROUP_FEATURE_QUAD_BIT

Float16

shaderFloat16

Int8

shaderInt8

StorageBuffer8BitAccess

StorageBuffer8BitAccess

UniformAndStorageBuffer8BitAccess

UniformAndStorageBuffer8BitAccess

StoragePushConstant8

StoragePushConstant8

VulkanMemoryModelKHR

vulkanMemoryModel

VulkanMemoryModelDeviceScopeKHR

vulkanMemoryModelDeviceScope

DenormPreserve

shaderDenormPreserveFloat16, shaderDenormPreserveFloat32, shaderDenormPreserveFloat64

DenormFlushToZero

shaderDenormFlushToZeroFloat16, shaderDenormFlushToZeroFloat32, shaderDenormFlushToZeroFloat64

SignedZeroInfNanPreserve

shaderSignedZeroInfNanPreserveFloat16, shaderSignedZeroInfNanPreserveFloat32, shaderSignedZeroInfNanPreserveFloat64

RoundingModeRTE

shaderRoundingModeRTEFloat16, shaderRoundingModeRTEFloat32, shaderRoundingModeRTEFloat64

RoundingModeRTZ

shaderRoundingModeRTZFloat16, shaderRoundingModeRTZFloat32, shaderRoundingModeRTZFloat64

The application can pass a SPIR-V module to vkCreateShaderModule that uses the SPV_KHR_variable_pointers SPIR-V extension.

The application can pass a SPIR-V module to vkCreateShaderModule that uses the SPV_KHR_shader_draw_parameters SPIR-V extension.

The application can pass a SPIR-V module to vkCreateShaderModule that uses the SPV_KHR_8bit_storage SPIR-V extension.

The application can pass a SPIR-V module to vkCreateShaderModule that uses the SPV_KHR_16bit_storage SPIR-V extension.

The application can pass a SPIR-V module to vkCreateShaderModule that uses the SPV_KHR_float_controls SPIR-V extension.

The application can pass a SPIR-V module to vkCreateShaderModule that uses the SPV_KHR_storage_buffer_storage_class SPIR-V extension.

The application can pass a SPIR-V module to vkCreateShaderModule that uses the SPV_KHR_vulkan_memory_model SPIR-V extension.

The application must not pass a SPIR-V module containing any of the following to 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.

Validation Rules within a Module

A SPIR-V module passed to 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:

  • Scope for Non Uniform Group Operations must be limited to:

    • Subgroup

  • Storage Class must be limited to:

    • UniformConstant

    • Input

    • Uniform

    • Output

    • Workgroup

    • Private

    • Function

    • PushConstant

    • Image

    • StorageBuffer

  • Memory semantics must obey the following rules:

    • Acquire must not be used with OpAtomicStore.

    • Release must not be used with OpAtomicLoad.

    • AcquireRelease must not be used with OpAtomicStore or OpAtomicLoad.

    • Sequentially consistent atomics and barriers are not supported and SequentiallyConsistent is treated as AcquireRelease. SequentiallyConsistent should not be used.

    • OpMemoryBarrier must use one of Acquire, Release, AcquireRelease, or SequentiallyConsistent and must include at least one storage class.

    • If the semantics for 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 OpVariable with an Initializer operand must have one of the following as its Storage Class operand:

    • Output

    • Private

    • Function

  • The OriginLowerLeft execution mode must not be used; fragment entry points must declare OriginUpperLeft.

  • The PixelCenterInteger execution mode must not be used. Pixels are always centered at half-integer coordinates.

  • Images and Samplers

    • OpTypeImage must declare a scalar 32-bit float or 32-bit integer type for the “Sampled Type”. (RelaxedPrecision can be applied to a sampling instruction and to the variable holding the result of a sampling instruction.)

    • OpTypeImage must have a “Sampled” operand of 1 (sampled image) or 2 (storage image).

    • If shaderStorageImageReadWithoutFormat is not enabled and an OpTypeImage has “Image Format” operand of Unknown, any variables created with the given type must be decorated with NonReadable.

    • If shaderStorageImageWriteWithoutFormat is not enabled and an OpTypeImage has “Image Format” operand of Unknown, any variables created with the given type must be decorated with NonWritable.

    • OpImageQuerySizeLod, and OpImageQueryLevels must only consume an “Image” operand whose type has its “Sampled” operand set to 1.

    • The (u,v) coordinates used for a SubpassData must be the <id> of a constant vector (0,0), or if a layer coordinate is used, must be a vector that was formed with constant 0 for the u and v components.

    • The “Depth” operand of OpTypeImage is ignored.

    • Objects of types OpTypeImage, OpTypeSampler, OpTypeSampledImage, and arrays of these types must not be stored to or modified.

  • Decorations

    • Any BuiltIn decoration not listed in Built-In Variables must not be used.

    • Any BuiltIn decoration that corresponds only to Vulkan features or extensions that have not been enabled must not be used.

    • The GLSLShared and GLSLPacked decorations must not be used.

    • The Flat, NoPerspective, Sample, and Centroid decorations must not be used on variables with storage class other than Input or on variables used in the interface of non-fragment shader entry points.

    • The Patch decoration must not be used on variables in the interface of a vertex, geometry, or fragment shader stage’s entry point.

    • Only the round-to-nearest-even and the round-to-zero rounding modes can be used for the FPRoundingMode decoration.

    • The FPRoundingMode decoration can only be used for the floating-point conversion instructions as described in the SPV_KHR_16bit_storage SPIR-V extension.

    • DescriptorSet and Binding decorations must obey the constraints on storage class, type, and descriptor type described in DescriptorSet and Binding Assignment

  • OpTypeRuntimeArray must only be used for:

    • the last member of an OpTypeStruct that is in the StorageBuffer storage class decorated as Block, or that is in the Uniform storage class decorated as BufferBlock.

  • Linkage: See Shader Interfaces for additional linking and validation rules.

  • If OpControlBarrier is used in fragment, vertex, tessellation evaluation, or geometry stages, the execution Scope must be Subgroup.

  • Compute Shaders

    • For each compute shader entry point, either a LocalSize execution mode or an object decorated with the WorkgroupSize decoration must be specified.

  • “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 Float64 capability is enabled, double and vectors of double types are also permitted.

  • If OpGroupNonUniformBallotBitCount is used, the group operation must be one of:

    • Reduce

    • InclusiveScan

    • ExclusiveScan

  • Atomic instructions must declare a scalar 32-bit integer type, or a scalar 64-bit integer type if the Int64Atomics capability is enabled, for the value pointed to by Pointer.

    • shaderBufferInt64Atomics must be enabled for 64-bit integer atomic operations to be supported on a Pointer with a Storage Class of StorageBuffer or Uniform.

    • shaderSharedInt64Atomics must be enabled for 64-bit integer atomic operations to be supported on a Pointer with a Storage Class of Workgroup.

  • The Pointer operand of all atomic instructions must have a Storage Class limited to:

    • Uniform

    • Workgroup

    • Image

    • StorageBuffer

  • If separateDenormSettings is VK_FALSE, then the entry point must use the same denormals execution mode for both 16-bit and 64-bit floating-point types.

  • If separateRoundingModeSettings is VK_FALSE, then the entry point must use the same rounding execution mode for both 16-bit and 64-bit floating-point types.

  • If shaderSignedZeroInfNanPreserveFloat16 is VK_FALSE, then SignedZeroInfNanPreserve for 16-bit floating-point type must not be used.

  • If shaderSignedZeroInfNanPreserveFloat32 is VK_FALSE, then SignedZeroInfNanPreserve for 32-bit floating-point type must not be used.

  • If shaderSignedZeroInfNanPreserveFloat64 is VK_FALSE, then SignedZeroInfNanPreserve for 64-bit floating-point type must not be used.

  • If shaderDenormPreserveFloat16 is VK_FALSE, then DenormPreserve for 16-bit floating-point type must not be used.

  • If shaderDenormPreserveFloat32 is VK_FALSE, then DenormPreserve for 32-bit floating-point type must not be used.

  • If shaderDenormPreserveFloat64 is VK_FALSE, then DenormPreserve for 64-bit floating-point type must not be used.

  • If shaderDenormFlushToZeroFloat16 is VK_FALSE, then DenormFlushToZero for 16-bit floating-point type must not be used.

  • If shaderDenormFlushToZeroFloat32 is VK_FALSE, then DenormFlushToZero for 32-bit floating-point type must not be used.

  • If shaderDenormFlushToZeroFloat64 is VK_FALSE, then DenormFlushToZero for 64-bit floating-point type must not be used.

  • If shaderRoundingModeRTEFloat16 is VK_FALSE, then RoundingModeRTE for 16-bit floating-point type must not be used.

  • If shaderRoundingModeRTEFloat32 is VK_FALSE, then RoundingModeRTE for 32-bit floating-point type must not be used.

  • If shaderRoundingModeRTEFloat64 is VK_FALSE, then RoundingModeRTE for 64-bit floating-point type must not be used.

  • If shaderRoundingModeRTZFloat16 is VK_FALSE, then RoundingModeRTZ for 16-bit floating-point type must not be used.

  • If shaderRoundingModeRTZFloat32 is VK_FALSE, then RoundingModeRTZ for 32-bit floating-point type must not be used.

  • If shaderRoundingModeRTZFloat64 is VK_FALSE, then RoundingModeRTZ for 64-bit floating-point type must not be used.

  • The Base operand of OpPtrAccessChain must point to one of the following storage classes:

    • Workgroup, if VariablePointers is enabled.

    • StorageBuffer, if VariablePointers or VariablePointersStorageBuffer is enabled.

    • PhysicalStorageBufferEXT, if the PhysicalStorageBuffer64EXT addressing model is enabled.

Precision and Operation of SPIR-V Instructions

The following rules apply to half, single, and double-precision floating point instructions:

  • Positive and negative infinities and positive and negative zeros are generated as dictated by IEEE 754, but subject to the precisions allowed in the following table.

  • Dividing a non-zero by a zero results in the appropriately signed IEEE 754 infinity.

  • Signaling NaNs are not required to be generated and exceptions are never raised. Signaling NaN may be converted to quiet NaNs values by any floating point instruction.

  • By default, the implementation may perform optimizations on half, single, or double-precision floating-point instructions respectively that ignore sign of a zero, or assume that arguments and results are not Nans or \(\pm\infty\), this doesn’t apply to OpIsNan and OpIsInf, which must always correctly detect Nans and \(\pm\infty\). If the entry point is declared with the SignedZeroInfNanPreserve execution mode, then sign of a zero, Nans, and \(\pm\infty\) must not be ignored.

    • The following core SPIR-V instructions must respect the SignedZeroInfNanPreserve execution mode: OpPhi, OpSelect, OpReturnValue, OpVectorExtractDynamic, OpVectorInsertDynamic, OpVectorShuffle, OpCompositeConstruct, OpCompositeExtract, OpCompositeInsert, OpCopyObject, OpTranspose, OpFConvert, OpFNegate, OpFAdd, OpFSub, OpFMul, OpStore. This execution mode must also be respected by OpLoad except for loads from the Input storage class in the fragment shader stage with the floating-point result type. Other SPIR-V instruction may also respect the SignedZeroInfNanPreserve execution mode.

  • Denormalized values are supported.

    • By default, any half, single, or double-precision denormalized value input into a shader or potentially generated by any instruction or any extended instructions for GLSL in a shader may be flushed to zero.

    • If the entry point is declared with the DenormFlushToZero execution mode then for the affected instuctions the denormalized result must be flushed to zero and the denormalized operands may be flushed to zero. Denormalized values obtained via unpacking an integer into a vector of values with smaller bit width and interpreting those values as floating-point numbers must be flushed to zero.

    • The following core SPIR-V instructions must respect the DenormFlushToZero execution mode: OpSpecConstantOp (except when the opcode is OpQuantizeToF16), OpFConvert, OpFNegate, OpFAdd, OpFSub, OpFMul, OpFDiv, OpFRem, OpFMod, OpVectorTimesScalar, OpMatrixTimesScalar, OpVectorTimesMatrix, OpMatrixTimesVector, OpMatrixTimesMatrix, OpOuterProduct, OpDot; and the following extended instructions for GLSL: Round, RoundEven, Trunc, FAbs, Floor, Ceil, Fract, Radians, Degrees, Sin, Cos, Tan, Asin, Acos, Atan, Sinh, Cosh, Tanh, Asinh, Acosh, Atanh, Atan2, Pow, Exp, Log, Exp2, Log2, Sqrt, InverseSqrt, Determinant, MatrixInverse, Modf, ModfStruct, FMin, FMax, FClamp, FMix, Step, SmoothStep, Fma, UnpackHalf2x16, UnpackDouble2x32, Length, Distance, Cross, Normalize, FaceForward, Reflect, Refract, NMin, NMax, NClamp. Other SPIR-V instruction may also respect the DenormFlushToZero execution mode.

    • The following core SPIR-V instructions must respect the DenormPreserve execution mode: OpPhi, OpSelect, OpReturnValue, OpVectorExtractDynamic, OpVectorInsertDynamic, OpVectorShuffle, OpCompositeConstruct, OpCompositeExtract, OpCompositeInsert, OpCopyObject, OpTranspose, OpStore, OpSpecConstantOp, OpFConvert, OpFNegate, OpFAdd, OpFSub, OpFMul, OpVectorTimesScalar, OpMatrixTimesScalar, OpVectorTimesMatrix, OpMatrixTimesVector, OpMatrixTimesMatrix, OpOuterProduct, OpDot, OpFOrdEqual, OpFUnordEqual, OpFOrdNotEqual, OpFUnordNotEqual, OpFOrdLessThan, OpFUnordLessThan, OpFOrdGreaterThan, OpFUnordGreaterThan, OpFOrdLessThanEqual, OpFUnordLessThanEqual, OpFOrdGreaterThanEqual, OpFUnordGreaterThanEqual; and the following extended instructions for GLSL: FAbs, FSign, Radians, Degrees, FMin, FMax, FClamp, FMix, Fma, PackHalf2x16, PackDouble2x32, UnpackHalf2x16, UnpackDouble2x32, NMin, NMax, NClamp. This execution mode must also be respected by OpLoad except for loads from the Input storage class in the fragment shader stage with the floating-point result type. Other SPIR-V instruction may also respect the DenormPreserve execution mode.

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, x, rounded so as to be representable in floating-point. The rounding mode is not specified, unless the entry point is declared with the RoundingModeRTE or the RoundingModeRTZ execution mode. These execution modes affect only correctly rounded SPIR-V instructions. These execution modes do not affect OpQuantizeToF16. If the rounding mode is not specified then this rounding is implementation specific, subject to the following rules. If x is exactly representable then x will be returned. Otherwise, either the floating-point value closest to and no less than x or the value closest to and no greater than x will be returned.

ULP

Where an error bound of 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 a ≤ x ≤ b then ulp(x) is the minimum possible distance between such numbers, \(ulp(x) = \mathrm{min}_{a,b} | b - a |\). 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, additionally, return either an infinity of the appropriate sign or the finite number with the largest magnitude 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 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 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 Fmax and the smallest be Fmin. The operation must return a value in the range [x - E, x + E] where \(E = \mathrm{max} \left( | x - F_{\mathrm{min}} |, | x - F_{\mathrm{max}} | \right) \). If the entry point is declared with the DenormFlushToZero execution mode, then any intermediate denormal value(s) while evaluating the formula may be flushed to zero. Denormal final results must be flushed to zero. If the entry point is declared with the DenormPreserve execution mode, then denormals must be preserved throughout the formula.

For half- (16 bit) and single- (32 bit) precision instructions, precisions are required to be at least as follows:

Table 66. Precision of core SPIR-V Instructions
Instruction Single precision, unless decorated with RelaxedPrecision Half precision

OpFAdd

Correctly rounded.

OpFSub

Correctly rounded.

OpFMul, OpVectorTimesScalar, OpMatrixTimesScalar

Correctly rounded.

OpDot(x, y)

Inherited from \(\sum_{i = 0}^{n - 1} x_{i} \times y_{i}\).

OpFOrdEqual, OpFUnordEqual

Correct result.

OpFOrdLessThan, OpFUnordLessThan

Correct result.

OpFOrdGreaterThan, OpFUnordGreaterThan

Correct result.

OpFOrdLessThanEqual, OpFUnordLessThanEqual

Correct result.

OpFOrdGreaterThanEqual, OpFUnordGreaterThanEqual

Correct result.

OpFDiv(x,y)

2.5 ULP for y in the range [2-126, 2126].

2.5 ULP for y in the range [2-14, 214].

OpFRem(x,y)

Inherited from x - y × trunc(x/y), for y in the range [2-126, 2126].

Inherited from x - y × trunc(x/y), for y in the range [2-14, 214].

OpFMod(x,y)

Inherited from x - y × floor(x/y), for y in the range [2-126, 2126].

Inherited from x - y × floor(x/y), for y in the range [2-14, 214].

conversions between types

Correctly rounded.
Note

The OpFRem and OpFMod instructions use cheap approximations of remainder, and the error can be large due to the discontinuity in trunc() and floor(). This can produce mathematically unexpected results in some cases, such as FMod(x,x) computing x rather than 0, and can also cause the result to have a different sign than the infinitely precise result.
Table 67. Precision of GLSL.std.450 Instructions
Instruction Single precision, unless decorated with RelaxedPrecision Half precision

fma()

Inherited from OpFMul followed by OpFAdd.

exp(x), exp2(x)

3 + 2 × |x| ULP.

1 + 2 × |x| ULP.

log(), log2()

3 ULP outside the range [0.5, 2.0]. Absolute error < 2-21 inside the range [0.5, 2.0].

3 ULP outside the range [0.5, 2.0]. Absolute error < 2-7 inside the range [0.5, 2.0].

pow(x, y)

Inherited from exp2(y × log2(x)).

sqrt()

Inherited from 1.0 / inversesqrt().

inversesqrt()

2 ULP.

radians(x)

Inherited from \(\frac{x \times \pi}{180}\).

degrees(x)

Inherited from \(\frac{x \times 180}{\pi}\).

sin()

Absolute error \(\leq 2^{-11}\) inside the range \([-\pi, \pi]\).

Absolute error \(\leq 2^{-7}\) inside the range \([-\pi, \pi]\).

cos()

Absolute error \(\leq 2^{-11}\) inside the range \([-\pi, \pi]\).

Absolute error \(\leq 2^{-7}\) inside the range \([-\pi, \pi]\).

tan()

Inherited from \(\frac{sin()}{cos()}\).

asin(x)

Inherited from \(atan2(x, sqrt(1.0 - x^2))\).

acos(x)

Inherited from \(atan2(sqrt(1.0 - x^2), x)\).

atan(), atan2()

4096 ULP

5 ULP.

sinh(x)

Inherited from \((exp(x) - exp(-x)) \times 0.5\).

cosh(x)

Inherited from \((exp(x) + exp(-x)) \times 0.5\).

tanh()

Inherited from \(\frac{sinh()}{cosh()}\).

asinh(x)

Inherited from \(log(x + sqrt(x^2 + 1.0))\).

acosh(x)

Inherited from \(log(x + sqrt(x^2 - 1.0))\).

atanh(x)

Inherited from \(log(\frac{1.0 + x}{1.0 - x}) \times 0.5\).

frexp()

Correctly rounded.

ldexp()

Correctly rounded.

length(x)

Inherited from \(sqrt(dot(x, x))\).

distance(x, y)

Inherited from \(length(x - y)\).

cross()

Inherited from OpFSub(OpFMul, OpFMul).

normalize(x)

Inherited from \(\frac{x}{length(x)}\).

faceforward

Correctly rounded.

reflect(x, y)

Inherited from x - 2.0 × dot(y, x) × y.

refract(I, N, eta)

Inherited from eta × I - (eta × dot(N, I) + sqrt(k)) × N.

round

Correctly rounded.

roundEven

Correctly rounded.

trunc

Correctly rounded.

fabs

Correctly rounded.

fsign

Correctly rounded.

floor

Correctly rounded.

ceil

Correctly rounded.

fract

Correctly rounded.

modf

Correctly rounded.

fmin

Correctly rounded.

fmax

Correctly rounded.

fclamp

Correctly rounded.

fmix(x, y, a)

Inherited from x × (1.0 - a) + y × a.

step

Correctly rounded.

smoothStep(edge0, edge1, x)

Inherited from t × t × (3.0 - 2.0 × t), where \(t = clamp(\frac{x - edge0}{edge1 - edge0}, 0.0, 1.0)\).

nmin

Correctly rounded.

nmax

Correctly rounded.

nclamp

Correctly rounded.

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 OpSRem and OpSMod instructions, if either operand is negative the result is undefined.

Note

While the OpSRem and OpSMod instructions are supported by the Vulkan environment, they require non-negative values and thus do not enable additional functionality beyond what OpUMod provides.

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 texture image validation. The compatibile formats are:

Table 68. SPIR-V and Vulkan Image Format Compatibility
SPIR-V Image Format Compatible Vulkan Format

Rgba32f

VK_FORMAT_R32G32B32A32_SFLOAT

Rgba16f

VK_FORMAT_R16G16B16A16_SFLOAT

R32f

VK_FORMAT_R32_SFLOAT

Rgba8

VK_FORMAT_R8G8B8A8_UNORM

Rgba8Snorm

VK_FORMAT_R8G8B8A8_SNORM

Rg32f

VK_FORMAT_R32G32_SFLOAT

Rg16f

VK_FORMAT_R16G16_SFLOAT

R11fG11fB10f

VK_FORMAT_B10G11R11_UFLOAT_PACK32

R16f

VK_FORMAT_R16_SFLOAT

Rgba16

VK_FORMAT_R16G16B16A16_UNORM

Rgb10A2

VK_FORMAT_A2B10G10R10_UNORM_PACK32

Rg16

VK_FORMAT_R16G16_UNORM

Rg8

VK_FORMAT_R8G8_UNORM

R16

VK_FORMAT_R16_UNORM

R8

VK_FORMAT_R8_UNORM

Rgba16Snorm

VK_FORMAT_R16G16B16A16_SNORM

Rg16Snorm

VK_FORMAT_R16G16_SNORM

Rg8Snorm

VK_FORMAT_R8G8_SNORM

R16Snorm

VK_FORMAT_R16_SNORM

R8Snorm

VK_FORMAT_R8_SNORM

Rgba32i

VK_FORMAT_R32G32B32A32_SINT

Rgba16i

VK_FORMAT_R16G16B16A16_SINT

Rgba8i

VK_FORMAT_R8G8B8A8_SINT

R32i

VK_FORMAT_R32_SINT

Rg32i

VK_FORMAT_R32G32_SINT

Rg16i

VK_FORMAT_R16G16_SINT

Rg8i

VK_FORMAT_R8G8_SINT

R16i

VK_FORMAT_R16_SINT

R8i

VK_FORMAT_R8_SINT

Rgba32ui

VK_FORMAT_R32G32B32A32_UINT

Rgba16ui

VK_FORMAT_R16G16B16A16_UINT

Rgba8ui

VK_FORMAT_R8G8B8A8_UINT

R32ui

VK_FORMAT_R32_UINT

Rgb10a2ui

VK_FORMAT_A2B10G10R10_UINT_PACK32

Rg32ui

VK_FORMAT_R32G32_UINT

Rg16ui

VK_FORMAT_R16G16_UINT

Rg8ui

VK_FORMAT_R8G8_UINT

R16ui

VK_FORMAT_R16_UINT

R8ui

VK_FORMAT_R8_UINT