python-pillow · hugovk · Aug 9, 2021 · Aug 7, 2021
diff --git a/Scripts/make_hash.py b/Scripts/make_hash.py
@@ -0,0 +1,66 @@
+# brute-force search for access descriptor hash table
+
+modes = [
+    "1",
+    "L",
+    "LA",
+    "La",
+    "I",
+    "I;16",
+    "I;16L",
+    "I;16B",
+    "I;32L",
+    "I;32B",
+    "F",
+    "P",
+    "PA",
+    "RGB",
+    "RGBA",
+    "RGBa",
+    "RGBX",
+    "CMYK",
+    "YCbCr",
+    "LAB",
+    "HSV",
+]
+
+
+def hash(s, i):
+    # djb2 hash: multiply by 33 and xor character
+    for c in s:
+        i = (((i << 5) + i) ^ ord(c)) & 0xFFFFFFFF
+    return i
+
+
+def check(size, i0):
+    h = [None] * size
+    for m in modes:
+        i = hash(m, i0)
+        i = i % size
+        if h[i]:
+            return 0
+        h[i] = m
+    return h
+
+
+min_start = 0
+
+# 1) find the smallest table size with no collisions
+for min_size in range(len(modes), 16384):
+    if check(min_size, 0):
+        print(len(modes), "modes fit in", min_size, "slots")
+        break
+
+# 2) see if we can do better with a different initial value
+for i0 in range(65556):
+    for size in range(1, min_size):
+        if check(size, i0):
+            if size < min_size:
+                print(len(modes), "modes fit in", size, "slots with start", i0)
+                min_size = size
+                min_start = i0
+
+print()
+
+print("#define ACCESS_TABLE_SIZE", min_size)
+print("#define ACCESS_TABLE_HASH", min_start)