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diff --git a/openpower/sv/svp_rewrite/svp64/discussion.mdwn b/openpower/sv/svp_rewrite/svp64/discussion.mdwn
index 4047962d7d5ac2f52e0b56e9726ee783a534bfb5..b336329213fcfadd84b48659e304513c6e51b881 100644 (file)
--- a/openpower/sv/svp_rewrite/svp64/discussion.mdwn
+++ b/openpower/sv/svp_rewrite/svp64/discussion.mdwn
@@ -33,26 +33,30 @@ something like:
 * ptyp - predication INT / CR
 * psrc / pdst - predicate mask selector and inversion
 * vspec - 3 bit src / dest scalar-vector extension
-* sat: DEFAULT / 8bit / 16bit / 32bit (signed/unsigned)
+* sat: 0bSU - S=1 signed U=1 unsigned 0b11 reserved
 
 # standard arith ops (single predication)
 
 these are of the form res = op(src1, src2, ...)
 
-| 0   1 | 2 3 | 4    | 5  7 | 8  16 | 17 19 |
-| ----- | --- | ---- | ---- | ----- | ----- |
-| subvl | ew  | ptyp | pred | vspec | sat   |
-
+| 0   1 | 2 3 | 4 5 | 6    | 7  9 | 10 18 | 19 21 |
+| ----- | --- | --- | ---- | ---- | ----- | ----- |
+| subvl | sew | dew | ptyp | pred | vspec | sat   |
 
 * subvl - 1 to 4 scalar / vec2 / vec3 / vec4
-* ew - DEFAULT / 8 / 16 /32 element width
+* sew / dew - DEFAULT / 8 / 16 /32 element width
 * ptyp - predication INT / CR
 * pred - predicate mask selector and inversion
 * vspec - 2/3 bit src / dest scalar-vector extension
-* sat: DEFAULT / 8bit / 16bit / 32bit (signed/unsigned)
+* sat: 0bSU - S=1 signed U=1 unsigned 0b11 reserved
 
 For 2 op (dest/src1/src2) the tag may be 3 bits: total 9 bits.  for 3 op (dest/src1/2/3) the vspec may be 2 bits per reg: total 8 bits.
 
+Note:
+
+* saturation is done on the result at the **source** elwidth
+* signed-saturation causes sign-extension from source to dest elwidths **after** saturation
+
 # Notes about rounding, clamp and saturate
 
 One of the issues with vector ops is that in integer DSP ops for example in Audio the operation must clamp or saturate rather than overflow or ignore the upper bits and become a modulo operation.  This for Audio is extremely important, also to provide an indicator as to whether saturation occurred.  see  [[av_opcodes]].