From 9a9b3fc161b90edace9143959db0708aaea52b6c Mon Sep 17 00:00:00 2001
From: Christopher Haster <geky@geky.net>
Date: Wed, 31 Jul 2024 12:17:13 -0500
Subject: [PATCH] scripts: Reverted crc32c.py to naive CRC implementation

The naive implementation is simpler, less code, and more likely to be
correct, each of these are more valuable than speed in our debug
scripts.

We're in Python anyways (no offense Python!).

Plus I think it's good to show that the underlying logic of CRCs aren't
really that complex, at least until we throw optimizations into the mix.
---
 scripts/crc32c.py | 76 +++--------------------------------------------
 1 file changed, 4 insertions(+), 72 deletions(-)

diff --git a/scripts/crc32c.py b/scripts/crc32c.py
index 9499d8fb..4301d1e8 100755
--- a/scripts/crc32c.py
+++ b/scripts/crc32c.py
@@ -16,82 +16,14 @@ def openio(path, mode='r', buffering=-1):
     else:
         return open(path, mode, buffering)
 
-# use big table here since we might as well try to go fast
-CRC32C_TABLE = [
-    0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4,
-    0xc79a971f, 0x35f1141c, 0x26a1e7e8, 0xd4ca64eb,
-    0x8ad958cf, 0x78b2dbcc, 0x6be22838, 0x9989ab3b,
-    0x4d43cfd0, 0xbf284cd3, 0xac78bf27, 0x5e133c24,
-    0x105ec76f, 0xe235446c, 0xf165b798, 0x030e349b,
-    0xd7c45070, 0x25afd373, 0x36ff2087, 0xc494a384,
-    0x9a879fa0, 0x68ec1ca3, 0x7bbcef57, 0x89d76c54,
-    0x5d1d08bf, 0xaf768bbc, 0xbc267848, 0x4e4dfb4b,
-    0x20bd8ede, 0xd2d60ddd, 0xc186fe29, 0x33ed7d2a,
-    0xe72719c1, 0x154c9ac2, 0x061c6936, 0xf477ea35,
-    0xaa64d611, 0x580f5512, 0x4b5fa6e6, 0xb93425e5,
-    0x6dfe410e, 0x9f95c20d, 0x8cc531f9, 0x7eaeb2fa,
-    0x30e349b1, 0xc288cab2, 0xd1d83946, 0x23b3ba45,
-    0xf779deae, 0x05125dad, 0x1642ae59, 0xe4292d5a,
-    0xba3a117e, 0x4851927d, 0x5b016189, 0xa96ae28a,
-    0x7da08661, 0x8fcb0562, 0x9c9bf696, 0x6ef07595,
-    0x417b1dbc, 0xb3109ebf, 0xa0406d4b, 0x522bee48,
-    0x86e18aa3, 0x748a09a0, 0x67dafa54, 0x95b17957,
-    0xcba24573, 0x39c9c670, 0x2a993584, 0xd8f2b687,
-    0x0c38d26c, 0xfe53516f, 0xed03a29b, 0x1f682198,
-    0x5125dad3, 0xa34e59d0, 0xb01eaa24, 0x42752927,
-    0x96bf4dcc, 0x64d4cecf, 0x77843d3b, 0x85efbe38,
-    0xdbfc821c, 0x2997011f, 0x3ac7f2eb, 0xc8ac71e8,
-    0x1c661503, 0xee0d9600, 0xfd5d65f4, 0x0f36e6f7,
-    0x61c69362, 0x93ad1061, 0x80fde395, 0x72966096,
-    0xa65c047d, 0x5437877e, 0x4767748a, 0xb50cf789,
-    0xeb1fcbad, 0x197448ae, 0x0a24bb5a, 0xf84f3859,
-    0x2c855cb2, 0xdeeedfb1, 0xcdbe2c45, 0x3fd5af46,
-    0x7198540d, 0x83f3d70e, 0x90a324fa, 0x62c8a7f9,
-    0xb602c312, 0x44694011, 0x5739b3e5, 0xa55230e6,
-    0xfb410cc2, 0x092a8fc1, 0x1a7a7c35, 0xe811ff36,
-    0x3cdb9bdd, 0xceb018de, 0xdde0eb2a, 0x2f8b6829,
-    0x82f63b78, 0x709db87b, 0x63cd4b8f, 0x91a6c88c,
-    0x456cac67, 0xb7072f64, 0xa457dc90, 0x563c5f93,
-    0x082f63b7, 0xfa44e0b4, 0xe9141340, 0x1b7f9043,
-    0xcfb5f4a8, 0x3dde77ab, 0x2e8e845f, 0xdce5075c,
-    0x92a8fc17, 0x60c37f14, 0x73938ce0, 0x81f80fe3,
-    0x55326b08, 0xa759e80b, 0xb4091bff, 0x466298fc,
-    0x1871a4d8, 0xea1a27db, 0xf94ad42f, 0x0b21572c,
-    0xdfeb33c7, 0x2d80b0c4, 0x3ed04330, 0xccbbc033,
-    0xa24bb5a6, 0x502036a5, 0x4370c551, 0xb11b4652,
-    0x65d122b9, 0x97baa1ba, 0x84ea524e, 0x7681d14d,
-    0x2892ed69, 0xdaf96e6a, 0xc9a99d9e, 0x3bc21e9d,
-    0xef087a76, 0x1d63f975, 0x0e330a81, 0xfc588982,
-    0xb21572c9, 0x407ef1ca, 0x532e023e, 0xa145813d,
-    0x758fe5d6, 0x87e466d5, 0x94b49521, 0x66df1622,
-    0x38cc2a06, 0xcaa7a905, 0xd9f75af1, 0x2b9cd9f2,
-    0xff56bd19, 0x0d3d3e1a, 0x1e6dcdee, 0xec064eed,
-    0xc38d26c4, 0x31e6a5c7, 0x22b65633, 0xd0ddd530,
-    0x0417b1db, 0xf67c32d8, 0xe52cc12c, 0x1747422f,
-    0x49547e0b, 0xbb3ffd08, 0xa86f0efc, 0x5a048dff,
-    0x8ecee914, 0x7ca56a17, 0x6ff599e3, 0x9d9e1ae0,
-    0xd3d3e1ab, 0x21b862a8, 0x32e8915c, 0xc083125f,
-    0x144976b4, 0xe622f5b7, 0xf5720643, 0x07198540,
-    0x590ab964, 0xab613a67, 0xb831c993, 0x4a5a4a90,
-    0x9e902e7b, 0x6cfbad78, 0x7fab5e8c, 0x8dc0dd8f,
-    0xe330a81a, 0x115b2b19, 0x020bd8ed, 0xf0605bee,
-    0x24aa3f05, 0xd6c1bc06, 0xc5914ff2, 0x37faccf1,
-    0x69e9f0d5, 0x9b8273d6, 0x88d28022, 0x7ab90321,
-    0xae7367ca, 0x5c18e4c9, 0x4f48173d, 0xbd23943e,
-    0xf36e6f75, 0x0105ec76, 0x12551f82, 0xe03e9c81,
-    0x34f4f86a, 0xc69f7b69, 0xd5cf889d, 0x27a40b9e,
-    0x79b737ba, 0x8bdcb4b9, 0x988c474d, 0x6ae7c44e,
-    0xbe2da0a5, 0x4c4623a6, 0x5f16d052, 0xad7d5351,
-]
-
 def crc32c(data, crc=0):
     crc ^= 0xffffffff
-
     for b in data:
-        crc = (crc >> 8) ^ CRC32C_TABLE[0xff & (crc ^ b)]
+        crc ^= b
+        for j in range(8):
+            crc = (crc >> 1) ^ ((crc & 1) * 0x82f63b78)
+    return 0xffffffff ^ crc
 
-    return crc ^ 0xffffffff
-    
 
 def main(paths, **args):
     # interpret as sequence of hex bytes