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[libreriscv.git] / zfpacc_proposal.mdwn

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+
 # FP Accuracy proposal
 
 Credits:
@@ -20,6 +21,20 @@ this proposal.  Only ULP (Unit in Last Place) of the instruction *result*
 is permitted to meet alternative accuracy requirements, whilst still
 retaining the instruction's requested format.
 
+This proposal is *only* suitable for adding pre-existing accuracy standards
+where it is clearly established, well in advance of applications being
+written that conform to that standard, that dealing with variations in
+accuracy across hardware implementations is the responsibility of the
+application writer.  This is the case for both Vulkan and OpenCL.
+
+This proposal is *not* suitable for inclusion of "de-facto" (proprietary)
+accuracy standards (historic IBM Mainframe vs Ahmdahl incompatibility)
+where there was no prior agreement or notification to applications
+writers that variations in accuracy across hardware implementations
+would occur.  In the unlikely event that they *are* ever to be included
+(n the future, rather than as a Custom Extension, then, unlike Vulkan
+and OpenCL, they must **only** be added as "bit-for-bit compatible".
+
 # Extension of FCSR
 
 Zfpacc would use some of the the reserved bits of FCSR.  It would be treated
@@ -151,6 +166,28 @@ Comments:
 
     <https://en.wikipedia.org/wiki/Minifloat>
 
+### function accuracy in standards (opencl, vulkan)
+
+[[resources]] for OpenCL and Vulkan
+
+Vulkan requires full ieee754 precision for all F/D instructions except for fdiv and fsqrt.
+
+<https://www.khronos.org/registry/vulkan/specs/1.1-extensions/html/chap40.html#spirvenv-precision-operation>
+
+Source is here:
+<https://github.com/KhronosGroup/Vulkan-Docs/blob/master/appendices/spirvenv.txt#L1172>
+
+OpenCL slightly different, suggest adding as an extra entry.
+
+<https://www.khronos.org/registry/OpenCL/specs/2.2/html/OpenCL_Env.html#relative-error-as-ulps>
+
+Link, finds version 2.1 of opencl environment specification, table 8.4.1 however needs checking if it is the same as the above, which has "SPIRV" in it and is 2.2 not 2.1
+
+https://www.google.com/search?q=opencl+environment+specification
+
+2.1 superceded by 2.2
+<https://github.com/KhronosGroup/OpenCL-Docs/blob/master/env/numerical_compliance.asciidoc>
+
 ### Compliance
 
 Dan Petroski: