From 0f02084805e1e24df85591be55af2d2108ec9d2f Mon Sep 17 00:00:00 2001
From: George Hotz <geohot@gmail.com>
Date: Sun, 25 Oct 2020 12:13:58 -0700
Subject: [PATCH] conv isn't fast yet

---
 tinygrad/utils.py | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/tinygrad/utils.py b/tinygrad/utils.py
index b926f2fcdd..330c64ee43 100644
--- a/tinygrad/utils.py
+++ b/tinygrad/utils.py
@@ -33,37 +33,50 @@ def fetch_mnist():
 # write them fast and the convs will be fast?
 
 @lru_cache
-def get_im2col_indexes(oy, ox, cin, H, W):
+def get_im2col_index(oy, ox, cin, H, W):
   idxc = np.tile(np.arange(cin).repeat(H*W), oy*ox)
   idxy = np.tile(np.arange(H).repeat(W), oy*ox*cin) + np.arange(oy).repeat(ox*cin*H*W)
   idxx = np.tile(np.arange(W), oy*ox*cin*H) + np.tile(np.arange(ox), oy).repeat(cin*H*W)
-  return idxc, idxy, idxx
+
+  # why return 3 index when we can return 1?
+  OY, OX = oy+(H-1), ox+(W-1)
+  idx = idxc * OY * OX + idxy * OX + idxx
+  return idx
 
 def im2col(x, H, W):
   bs,cin,oy,ox = x.shape[0], x.shape[1], x.shape[2]-(H-1), x.shape[3]-(W-1)
 
-  ic, iy, ix = get_im2col_indexes(oy, ox, cin, H, W)
-  tx = x[:, ic, iy, ix]
+  idx = get_im2col_index(oy, ox, cin, H, W)
+  tx = x.reshape(bs, -1)[:, idx]
+
+  """
+  # this is slower
+  tx = np.empty((bs, oy, ox, cin*W*H), dtype=x.dtype)
+  for Y in range(oy):
+    for X in range(ox):
+      tx[:, Y, X] = x[:, :, Y:Y+H, X:X+W].reshape(bs, -1)
+  """
+
   return tx.reshape(-1, cin*W*H)
 
 def col2im(tx, H, W, OY, OX):
   oy, ox = OY-(H-1), OX-(W-1)
   bs = tx.shape[0] // (oy * ox)
   cin = tx.shape[1] // (H * W)
-  x = np.zeros((bs, cin, OY, OX), dtype=tx.dtype)
 
   """
   # col2im is just im2col in reverse
-  tx = tx.reshape(bs, -1)
-  ic, iy, ix = get_im2col_indexes(oy, ox, cin, H, W)
-  np.add.at(x, (slice(None), ic, iy, ix), tx)
+  x = np.zeros((bs, cin*OY*OX), dtype=tx.dtype)
+  idx = get_im2col_index(oy, ox, cin, H, W)
+  np.add.at(x, (slice(None), idx), tx.reshape(bs, -1))
   """
 
   # sadly, this is faster
+  x = np.zeros((bs, cin, OY, OX), dtype=tx.dtype)
   tx = tx.reshape(bs, oy, ox, cin, H, W)
   for Y in range(oy):
     for X in range(ox):
       x[:, :, Y:Y+H, X:X+W] += tx[:, Y, X]
 
-  return x
+  return x.reshape(bs, cin, OY, OX)