From: lkcl Date: Thu, 9 Sep 2021 11:49:30 +0000 (+0100) Subject: (no commit message) X-Git-Tag: DRAFT_SVP64_0_1~172 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=14cbe3fbf03637113996fec0b26231f6f13ea5c9;p=libreriscv.git --- diff --git a/openpower/sv/cr_ops.mdwn b/openpower/sv/cr_ops.mdwn index 7f5dd8d2c..4c1363652 100644 --- a/openpower/sv/cr_ops.mdwn +++ b/openpower/sv/cr_ops.mdwn @@ -65,8 +65,15 @@ TODO # Data-dependent fail-first on CR operations +The principle of data-dependent fail-first is that if a Condition Test +fails then VL (Vector Length) is truncated at that point. In the case +of Arithmetic SVP64 Operations the Condition Register Field generated from +Rc=1 is used, however with CR-based operations that CR result is provided +by the operation itself. In some cases however, CR-based operations +operate on entire CR fields, not just one bit. + Data-dependent SVP64 Vectorised Operations involving the creation or -modification of a CR require an extra two bits, which are not available +modification of a CR can require an extra two bits, which are not available in the compact space of the `MODE` Field. With the concept of element width overrides being meaningless for CR Fields it is possible to use the `ELWIDTH` field for extra fields.