From: lkcl <lkcl@web>
Date: Sun, 12 Jun 2022 16:07:52 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~1825
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=cfcf0bfc5f63e5f30193ca54a52be023a3b187fa;p=libreriscv.git

---

diff --git a/openpower/sv/mv.swizzle.mdwn b/openpower/sv/mv.swizzle.mdwn
index 0c9e66c11..b54ceac5a 100644
--- a/openpower/sv/mv.swizzle.mdwn
+++ b/openpower/sv/mv.swizzle.mdwn
@@ -17,6 +17,15 @@ A compromise is to provide a Swizzle "Move".
 The encoding for this instruction embeds static predication into the
 swizzle as well as constants 1/1.0 and 0/0.0
 
+Although conceptually similar to `vpermd` of Packed SIMD VSX,
+Swizzle Moves come in immediate-only form with only up to four
+selectors, where VSX refers to individual bytes and may not
+copy constants to the destination.
+3D Shader programs commonly use the letters "XYZW"
+when referring to the four swizzle indices, and also often
+use the letters "RGBA"
+if referring to pixel data.
+
 # Format
 
 | 0.5 |6.10|11.15|16.27|28.31|  name        | Form    |
@@ -32,6 +41,7 @@ to each:
 | imm   |0.2 |3.5 |6.8|9.11|
 |-------|----|----|---|----|
 |swizzle|X   | Y  | Z | W  |
+|pixel  |R   | G  | B | A  |
 |index  |0   | 1  | 2 | 3  |
 
 the options for each Swizzle are:
@@ -70,7 +80,7 @@ mv.swiz and fmv.swiz operate on four 32-bit
 quantities, reducing this instruction to 2-in, 2-out pairs of 64-bit
 registers:
 
-| swizzle name | source | dest | half   |
+| swizzle name | source | dest | half    |
 |--            | --     | --   | --      |
 | X            | RA     | RT   | lo-half |
 | Y            | RA     | RT   | hi-half |
@@ -92,6 +102,11 @@ an Exception or Interrupt may not occur during the pair of Moves.
 
 **SVP64 Vectorised**
 
+Vectorised Swizzle may be considered to be an extended static predicate
+mask for subvectors (SUBVL=2/3/4). SUBVL (and SRC_SUBVL, see later section)
+must be set in order to aid in determining source and destination subvector
+lengths.
+
 When Vectorised, given the use-case is for a High-performance GPU,
 the fundamental assumption is that Micro-coding or
 other technique will
@@ -130,6 +145,12 @@ permitted
 to be serviced. Out-of-Order Micro-architectures may of course cancel
 the in-flight instruction as usual if the Interrupt requires fast servicing.
 
+Swizzle Pseudocode (when SRC_SUBVL=SUBVL):
+
+```
+```
+
+
 # RM Mode Concept:
 
 MVRM-2P-2S1D:
@@ -171,9 +192,14 @@ For a separate source/dest SUBVL (again, no elwidth overrides):
             for i in range(VL):
                 yield i+VL*j
 
-    # walk through both source and dest indices simultaneously
-    for src_idx, dst_idx in zip(index_src(), index_dst()):
-        move_operation(RT+dst_idx, RA+src_idx)
+    # inner looping when SUBVLs are equal
+    if SRC_SUBVL == SUBVL:
+        for idx in index():
+            move_operation(RT+idx, RA+idx)
+    else:
+        # walk through both source and dest indices simultaneously
+        for src_idx, dst_idx in zip(index_src(), index_dst()):
+            move_operation(RT+dst_idx, RA+src_idx)
 
 "yield" from python is used here for simplicity and clarity.
 The two Finite State Machines for the generation of the source