Use SIGNED instead of NATURAL for c_half. Now use s_round() to implement...

Use SIGNED instead of NATURAL for c_half. Now use s_round() to implement u_round() to have cleaner code.

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

@@ -2385,24 +2385,23 @@ PACKAGE BODY common_pkg IS
     -- #   floor(vec + 0.5)  -4    -3    -2    -1    1    2    3    4
     -- #   round even        -4    -2    -2     0    0    2    2    4
     -- #   round even clip   -4    -2    -2     0    0    2    2    3, clip to c_clip = 3 when c_out_w = 3
-    -- v_out = floor(vec + 0.5)
-    -- if fraction = 0.5 and v_out = odd:
-    --   v_out -= 1
-    -- Use SIGNED to avoid NATURAL (32 bit range) overflow error
+    -- Use SIGNED instead of NATURAL for c_half to avoid INTEGER (32 bit range) overflow error
     CONSTANT c_in_w     : NATURAL := vec'LENGTH;
     CONSTANT c_out_w    : NATURAL := vec'LENGTH - n;
-    CONSTANT c_half     : NATURAL := 2**(n-1);
-    CONSTANT c_max      : INTEGER := 2**(c_in_w-1)-1 - c_half;
-    CONSTANT c_clip     : INTEGER := 2**(c_out_w-1)-1;
-    CONSTANT s_clip     : SIGNED(c_out_w-1 DOWNTO 0) := TO_SIGNED(c_clip, c_out_w);
+    CONSTANT c_one      : SIGNED(c_in_w-1 DOWNTO 0) := TO_SIGNED(1, c_in_w);
+    CONSTANT c_half     : SIGNED(c_in_w-1 DOWNTO 0) := SHIFT_LEFT(c_one, n-1);                            -- = 2**(n-1)
+    CONSTANT c_max      : SIGNED(c_in_w-1 DOWNTO 0) := SIGNED('0' & c_slv1(c_in_w-2 DOWNTO 0)) - c_half;  -- = 2**(c_in_w-1)-1 - c_half
+    -- When c_out_w = 1, then c_clip = 0, because a 1 bit signed value is -1 or 0
+    CONSTANT c_clip     : SIGNED(c_out_w-1 DOWNTO 0) := SIGNED('0' & c_slv1(c_out_w-2 DOWNTO 0));         -- = 2**(c_out_w-1)-1
     VARIABLE v_in       : SIGNED(c_in_w-1 DOWNTO 0);
-    VARIABLE v_fraction : UNSIGNED(n-1 DOWNTO 0);
+    CONSTANT u_half     : UNSIGNED(n-1 DOWNTO 0) := UNSIGNED(STD_LOGIC_VECTOR(c_half(n-1 DOWNTO 0)));     -- convert to UNSIGNED to compare with u_fraction
+    VARIABLE u_fraction : UNSIGNED(n-1 DOWNTO 0);
     VARIABLE v_out      : SIGNED(c_out_w-1 DOWNTO 0);
   BEGIN
     v_in := SIGNED(vec);
     IF n > 0 THEN
       IF clip = TRUE AND v_in > c_max THEN
-        v_out := s_clip;  -- Round clip to maximum positive to avoid wrap to negative
+        v_out := c_clip;  -- Round clip to maximum positive to avoid wrap to negative
       ELSE
         IF even = FALSE THEN
           -- Round half away
@@ -2414,8 +2413,8 @@ PACKAGE BODY common_pkg IS
         ELSE
           -- Round half to even
           v_out := RESIZE_NUM(SHIFT_RIGHT(v_in + c_half, n), c_out_w);  -- Round to nearest using floor(vec + 0.5)
-          v_fraction := UNSIGNED(vec(n-1 DOWNTO 0));
-          IF v_fraction = c_half AND v_out(0) = '1' THEN  -- Round half to even, so when odd subtract 1
+          u_fraction := UNSIGNED(vec(n-1 DOWNTO 0));
+          IF u_fraction = u_half AND v_out(0) = '1' THEN  -- Round half to even, so when odd subtract 1
             v_out := v_out - 1;                           -- to make v_out even
           END IF;
         END IF;
@@ -2436,50 +2435,17 @@ PACKAGE BODY common_pkg IS
     RETURN s_round(vec, n, FALSE);  -- no round clip
   END;
   
-  -- Unsigned numbers are round up (almost same as s_round, but without the else on negative vec)
+  -- for unsigned round half away and round half up are equivalent
   FUNCTION u_round(vec : STD_LOGIC_VECTOR; n : NATURAL; clip, even : BOOLEAN) RETURN STD_LOGIC_VECTOR IS
-    -- # Round half up when even = FALSE, else round half to even.
-    -- # Round half to even algorithm:
-    -- #                vec: 0.5  1.5  2.5  3.5  4.5  5.5  6.5  7.5
-    -- #   floor(vec + 0.5)  1    2    3    4    5    6    7    8
-    -- #   round even        0    2    2    4    4    6    6    8
-    -- #   round even clip   0    2    2    4    4    6    6    7, clip to c_clip = 7 when c_out_w = 3
-    -- v_out = floor(vec + 0.5)
-    -- if fraction = 0.5 and v_out = odd:
-    --   v_out -= 1
-    --
-    -- Use UNSIGNED to avoid NATURAL (32 bit range) overflow error
     CONSTANT c_in_w     : NATURAL := vec'LENGTH;
     CONSTANT c_out_w    : NATURAL := vec'LENGTH - n;
-    CONSTANT c_half     : NATURAL := 2**(n-1);
-    CONSTANT c_max      : NATURAL := 2**c_in_w-1 - c_half;
-    CONSTANT c_clip     : NATURAL := 2**c_out_w-1;
-    CONSTANT u_clip     : UNSIGNED(c_out_w-1 DOWNTO 0) := TO_UNSIGNED(c_clip, c_out_w);
-    VARIABLE v_in       : UNSIGNED(c_in_w-1 DOWNTO 0);
-    VARIABLE v_fraction : UNSIGNED(n-1 DOWNTO 0);
-    VARIABLE v_out      : UNSIGNED(c_out_w-1 DOWNTO 0);
-  BEGIN
-    v_in := UNSIGNED(vec);
-    IF n > 0 THEN
-      IF clip = TRUE AND v_in > c_max THEN
-        v_out := u_clip;  -- Round clip to +max to avoid wrap to 0
-      ELSE
-        IF even = FALSE THEN
-          -- Round half up
-          v_out := RESIZE_NUM(SHIFT_RIGHT(v_in + c_half, n), c_out_w);  -- Round half up using floor(vec + 0.5)
-        ELSE
-          -- Round half to even
-          v_out := RESIZE_NUM(SHIFT_RIGHT(v_in + c_half, n), c_out_w);  -- Round to nearest using floor(vec + 0.5)
-          v_fraction := UNSIGNED(vec(n-1 DOWNTO 0));
-          IF v_fraction = c_half AND v_out(0) = '1' THEN  -- Round half to even, so when odd subtract 1
-            v_out := v_out - 1;                           -- to make v_out even
-          END IF;
-        END IF;
-      END IF;
-    ELSE
-      v_out := RESIZE_NUM(v_in, c_out_w);  -- NOP
-    END IF;
-    RETURN STD_LOGIC_VECTOR(v_out);
+    VARIABLE in_vec     : STD_LOGIC_VECTOR(c_in_w DOWNTO 0);
+    VARIABLE out_vec    : STD_LOGIC_VECTOR(c_out_w DOWNTO 0);
+  BEGIN
+    -- Convert unsigned to positive signed and back to be able to reuse s_round()
+    in_vec := '0' & vec;
+    out_vec := s_round(in_vec, n, clip, even);
+    RETURN out_vec(c_out_w-1 DOWNTO 0);
   END;
 
   FUNCTION u_round(vec : STD_LOGIC_VECTOR; n : NATURAL; clip : BOOLEAN) RETURN STD_LOGIC_VECTOR IS