add code which prints tables for shift

diff --git a/3d_gpu/architecture/dynamic_simd/shift.mdwn b/3d_gpu/architecture/dynamic_simd/shift.mdwn
index a4be80f7c2859e47b668a94487ea6a2bb255e505..337cd4b197d364ec6ec4eaaa0de0854bf33458c8 100644 (file)
--- a/3d_gpu/architecture/dynamic_simd/shift.mdwn
+++ b/3d_gpu/architecture/dynamic_simd/shift.mdwn
@@ -115,6 +115,43 @@ For o3:
     if      p1&~p2:   o3 |= a3b2[7:0]
     if          p2:   o3 |= a3b3[7:0]
 
+Code that prints the above:
+
+    def decoderange(col, k):
+        xs = (col-k)*8
+        return "%d:%d" % (xs+7, xs)
+
+    def decodelist(l):
+        res = []
+        for (idx, sgn) in l:
+            sgn = " " if sgn else "~"
+            res.append("%sp%d" % (sgn, idx))
+        return '&'.join(res)
+
+    N = 4
+    M = 4
+
+    for col in range(M):
+        r = decoderange(col, 0)
+        print "if True: o%d = a0b0[%s]" % (col, r)
+        for i in range(1,col+1):
+            l = []
+            for j in range(i):
+                l.append([j, False])
+            k = 0
+            s = decodelist(l)
+            r = decoderange(col, i)
+            print "if %s: o%d |= a%db%d[%s]" % (s, col, i, k, r)
+            k += 1
+            while l:
+                l[0][1] = True
+                s = decodelist(l)
+                r = decoderange(col, i)
+                print "if %s: o%d |= a%db%d[%s]" % (s, col, i, k, r)
+                k += 1
+                del l[0]
+        print
+
 ## Note
 
 One important part to remember is that the upper bits of the shift amount need to specifically *ignored* rather than assuming that they are zeros, this is because, for shift instructions: `a << b` actually is `a << (b % bit_len(a))`