From: Luke Kenneth Casson Leighton Date: Mon, 16 Apr 2018 05:33:40 +0000 (+0100) Subject: add SIMD comparison section X-Git-Tag: convert-csv-opcode-to-binary~5659 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=5ee4f27a9e775ddf1a8087e993a185c7ce840278;hp=dc5878b91bf6eae9a64d8ff5b45c8626a61f0ba5;p=libreriscv.git add SIMD comparison section --- diff --git a/simple_v_extension.mdwn b/simple_v_extension.mdwn index a20010aa4..47e2d54fd 100644 --- a/simple_v_extension.mdwn +++ b/simple_v_extension.mdwn @@ -1218,7 +1218,28 @@ the question is asked "How can each of the proposals effectively implement topologically transplant every single instruction from RVV (as designed) into Simple-V equivalents, with *zero loss of functionality or capability*. - +* With the "parallelism" abstracted out, a "DSP" Extension which contained + the basic primitives (non-parallelised 8, 16 or 32-bit SIMD operations) + inherently *become* parallel, automatically. +* Whilst not entirely finalised, registers are expected to be + capable of being subdivided down to an implementor-chosen bitwidth + in the underlying hardware (r1 becomes r1[31..24] r1[23..16] r1[15..8] + and r1[7..0], or just r1[31..16] r1[15..0]) where implementors can + choose to have separate independent 8-bit ALUs or dual-SIMD 16-bit + ALUs that perform twin 8-bit operations as they see fit, or anything + else including no subdivisions at all. +* Even though implementors have that choice even to have full 64-bit + (with RV64) SIMD, they *must* provide predication that transparently + switches off the required units on the last loop, thus neatly fitting + underlying SIMD ALU implementations *into* the RVV paradigm, keeping + the uniform consistent API that is a key strategic feature of Simple-V. +* With Simple-V fitting into the standard register files, certain classes + of SIMD operations such as High/Low arithmetic (r1[31..16] + r2[15..0]) + can be done by applying *Parallelised* Bit-manipulation operations + followed by parallelised *straight* versions of element-to-element + arithmetic operations, even if the bit-manipulation operations require + changing the bitwidth of the "vectors" to do so. Predication can + be utilised to skip high words (or low words) in source or destination. # Impementing V on top of Simple-V