From: lkcl <lkcl@web>
Date: Sat, 12 Mar 2022 11:55:42 +0000 (+0000)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~3090
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=b73bd117d8840b1257b7c75f9d2e89f233085ee0;p=libreriscv.git

---

diff --git a/openpower/sv/bitmanip.mdwn b/openpower/sv/bitmanip.mdwn
index 8bfeab0cb..2467873f4 100644
--- a/openpower/sv/bitmanip.mdwn
+++ b/openpower/sv/bitmanip.mdwn
@@ -187,24 +187,26 @@ mode (3 bit) may be used to do inversion of ordering, similar to carryless mul,
 
 ## ternlogv
 
-also, another possible variant involving swizzle and vec4:
+also, another possible variant involving swizzle-like selection
+and masking, this only requires 2 64 bit registers (RA, RT) and
+only up to 16 LUT3s
 
 | 0.5|6.10|11.15| 16.23 |24.27 | 28.30 |31|
 | -- | -- | --- | ----- | ---- | ----- |--|
 | NN | RT | RA  | idx0-3| mask | sz 01   |0 |
 
-    SZ = sz * 8
-    raoff = idx0 * SZ
-    rboff = idx0 * SZ
-    rcoff = idx0 * SZ
-    imoff = idx0 * SZ
+    SZ = (1+sz) * 8 # 8 or 16
+    raoff = MIN(XLEN, idx0 * SZ)
+    rboff = MIN(XLEN, idx1 * SZ)
+    rcoff = MIN(XLEN, idx2 * SZ)
+    imoff = MIN(XLEN, idx3 * SZ)
     imm = RA[imoff:imoff+SZ]
-    for i in range(SZ):
+    for i in range(MIN(XLEN, SZ)):
         ra = RA[raoff:+i]
         rb = RA[rboff+i]
         rc = RA[rcoff+i]
         res = lut3(imm, ra, rb, rc)
-        for j in range(3):
+        for j in range(MIN(XLEN//8, 4)):
              if mask[j]: RT[i+j*SZ] = res
 
 ## ternlogcr