Added comments to RESIZE_NUM(), no functional change.

libraries/base/common/src/vhdl/common_pkg.vhd

@@ -388,7 +388,10 @@ PACKAGE common_pkg IS
   -- appropriate approach is to ignore the MSbit sign and just keep the LS part. For too large values this 
   -- means that the result gets wrapped, but that is fine for default behaviour, because that is also what
   -- happens for RESIZE of UNSIGNED. Therefor this is what the RESIZE_NUM for SIGNED and the RESIZE_SVEC do
-  -- and better not use RESIZE for SIGNED anymore.
+  -- and better not use RESIZE for SIGNED anymore. When w keeps or increases the data width then the values
+  -- do not change (of course). When w reduces the data width then:
+  -- * RESIZE() wraps between -, 0 for negative and 0, + for positive, so it keeps the sign and w-1 LSbits
+  -- * RESIZE_NUM() removes MSbits, so it wraps from + to - and from - to +, and it keeps the w LSbits
   FUNCTION RESIZE_NUM( u   : UNSIGNED;         w : NATURAL) RETURN UNSIGNED;          -- left extend with '0' or keep LS part (same as RESIZE for UNSIGNED)
   FUNCTION RESIZE_NUM( s   : SIGNED;           w : NATURAL) RETURN SIGNED;            -- extend sign bit or keep LS part
   FUNCTION RESIZE_UVEC(sl  : STD_LOGIC;        w : NATURAL) RETURN STD_LOGIC_VECTOR;  -- left extend with '0' into slv
@@ -1975,8 +1978,8 @@ PACKAGE BODY common_pkg IS
   
   FUNCTION RESIZE_NUM(u : UNSIGNED; w : NATURAL) RETURN UNSIGNED IS
   BEGIN
-    -- left extend with '0' or keep LS part (same as RESIZE for UNSIGNED)
-    RETURN RESIZE(u, w);
+    -- left extend with '0' or remove MSbits and keep LS part (= u[w-1:0])
+    RETURN RESIZE(u, w);   -- same as RESIZE for UNSIGNED
   END;
   
   FUNCTION RESIZE_NUM(s : SIGNED; w : NATURAL) RETURN SIGNED IS
@@ -1985,7 +1988,12 @@ PACKAGE BODY common_pkg IS
     IF w>s'LENGTH THEN
       RETURN RESIZE(s, w);                    -- extend sign bit
     ELSE
-      RETURN SIGNED(RESIZE(UNSIGNED(s), w));  -- keep LSbits (= vec[w-1:0])
+      -- RESIZE() wraps between -, 0 for negative and 0, + for positive, so it keeps the sign and w-1 LSbits
+      -- RESIZE_NUM() removes MSbits, so it wraps from + to - and from - to +, and it keeps the w LSbits
+
+      -- remove MSbits and keep LS part (= s[w-1:0])
+      -- use RESIZE(UNSIGNED()) rather than s[w-1:0] to be independent of RANGE of s
+      RETURN SIGNED(RESIZE(UNSIGNED(s), w));
     END IF;
   END;