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[PATCH] Add crc32 function


From: John Darrington
Subject: [PATCH] Add crc32 function
Date: Wed, 27 Nov 2019 17:28:55 +0100

        * src/std.pk (crc32): New function.
        * doc/poke.texi (CRC Functions): New node.
---
 ChangeLog     |  5 +++++
 doc/poke.texi | 22 ++++++++++++++++++++++
 src/std.pk    | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 85 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index d78d76f..4a4651f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2019-11-24 John Darrington <address@hidden>
+
+        * src/std.pk (crc32): New function.
+        * doc/poke.texi (CRC Functions): New node.
+
 2019-11-27  Jose E. Marchesi  <address@hidden>
 
        * src/pvm.jitter (quake): New instruction.
diff --git a/doc/poke.texi b/doc/poke.texi
index ce65847..9576a04 100644
--- a/doc/poke.texi
+++ b/doc/poke.texi
@@ -108,6 +108,7 @@ The Standard Library
 * Conversion Functions::       catos, atoi, etc.
 * String Functions::           Functions which deal with strings.
 * Sorting Functions::          qsort.
+* CRC Functions::               Cyclic Redundancy Checksums.
 
 Hacking poke
 * Writing Commands::           Extending poke with new commands.
@@ -3917,6 +3918,27 @@ prototype:
 deftype Comparator = (any,any):int;
 @end example
 
+@node CRC Functions
+@chapter CRC Functions
+@cindex CRC
+@cindex checksum
+
+Many file formats use checksums of one sort or another.
+Therefore you may want to write such a checksum or verify
+a checksum in a constrained field. @xref{Field Constraints}.
+
+Some formats use simple additive checksums.  Another common checksum
+is the Cyclic Redundancy Checksum (CRC).  The standard function
+@code{crc32} calculates the 32 bit CRC defined by ISO-3309.
+
+@example
+defun crc32 = (byte[] @var{buf}) uint<32>: @{ @dots{} @}
+@end example
+
+@noindent
+This function returns the 32 bit CRC for the data contained in the
+array @var{buf}.
+
 @node Writing Commands
 @chapter Writing Commands
 
diff --git a/src/std.pk b/src/std.pk
index 5a87cf5..0da1b93 100644
--- a/src/std.pk
+++ b/src/std.pk
@@ -165,6 +165,64 @@ defun qsort = (any[] array, Comparator cmp_f,
    }
 }
 
+/*** CRC functions.  */
+
+/*
+   See ISO 3309 [ISO-3309] or ITU-T V.42 [ITU-V42] for a formal specification.
+*/
+
+defun crc32 = (byte[] buf) uint<32>:
+  {
+   defun update = (uint<32> crc, byte[] buf) uint<32>:
+   {
+    defvar table =
+    [
+     0x00000000U, 0x77073096U, 0xee0e612cU, 0x990951baU, 0x076dc419U, 
0x706af48fU, 0xe963a535U, 0x9e6495a3U,
+     0x0edb8832U, 0x79dcb8a4U, 0xe0d5e91eU, 0x97d2d988U, 0x09b64c2bU, 
0x7eb17cbdU, 0xe7b82d07U, 0x90bf1d91U,
+     0x1db71064U, 0x6ab020f2U, 0xf3b97148U, 0x84be41deU, 0x1adad47dU, 
0x6ddde4ebU, 0xf4d4b551U, 0x83d385c7U,
+     0x136c9856U, 0x646ba8c0U, 0xfd62f97aU, 0x8a65c9ecU, 0x14015c4fU, 
0x63066cd9U, 0xfa0f3d63U, 0x8d080df5U,
+     0x3b6e20c8U, 0x4c69105eU, 0xd56041e4U, 0xa2677172U, 0x3c03e4d1U, 
0x4b04d447U, 0xd20d85fdU, 0xa50ab56bU,
+     0x35b5a8faU, 0x42b2986cU, 0xdbbbc9d6U, 0xacbcf940U, 0x32d86ce3U, 
0x45df5c75U, 0xdcd60dcfU, 0xabd13d59U,
+     0x26d930acU, 0x51de003aU, 0xc8d75180U, 0xbfd06116U, 0x21b4f4b5U, 
0x56b3c423U, 0xcfba9599U, 0xb8bda50fU,
+     0x2802b89eU, 0x5f058808U, 0xc60cd9b2U, 0xb10be924U, 0x2f6f7c87U, 
0x58684c11U, 0xc1611dabU, 0xb6662d3dU,
+     0x76dc4190U, 0x01db7106U, 0x98d220bcU, 0xefd5102aU, 0x71b18589U, 
0x06b6b51fU, 0x9fbfe4a5U, 0xe8b8d433U,
+     0x7807c9a2U, 0x0f00f934U, 0x9609a88eU, 0xe10e9818U, 0x7f6a0dbbU, 
0x086d3d2dU, 0x91646c97U, 0xe6635c01U,
+     0x6b6b51f4U, 0x1c6c6162U, 0x856530d8U, 0xf262004eU, 0x6c0695edU, 
0x1b01a57bU, 0x8208f4c1U, 0xf50fc457U,
+     0x65b0d9c6U, 0x12b7e950U, 0x8bbeb8eaU, 0xfcb9887cU, 0x62dd1ddfU, 
0x15da2d49U, 0x8cd37cf3U, 0xfbd44c65U,
+     0x4db26158U, 0x3ab551ceU, 0xa3bc0074U, 0xd4bb30e2U, 0x4adfa541U, 
0x3dd895d7U, 0xa4d1c46dU, 0xd3d6f4fbU,
+     0x4369e96aU, 0x346ed9fcU, 0xad678846U, 0xda60b8d0U, 0x44042d73U, 
0x33031de5U, 0xaa0a4c5fU, 0xdd0d7cc9U,
+     0x5005713cU, 0x270241aaU, 0xbe0b1010U, 0xc90c2086U, 0x5768b525U, 
0x206f85b3U, 0xb966d409U, 0xce61e49fU,
+     0x5edef90eU, 0x29d9c998U, 0xb0d09822U, 0xc7d7a8b4U, 0x59b33d17U, 
0x2eb40d81U, 0xb7bd5c3bU, 0xc0ba6cadU,
+     0xedb88320U, 0x9abfb3b6U, 0x03b6e20cU, 0x74b1d29aU, 0xead54739U, 
0x9dd277afU, 0x04db2615U, 0x73dc1683U,
+     0xe3630b12U, 0x94643b84U, 0x0d6d6a3eU, 0x7a6a5aa8U, 0xe40ecf0bU, 
0x9309ff9dU, 0x0a00ae27U, 0x7d079eb1U,
+     0xf00f9344U, 0x8708a3d2U, 0x1e01f268U, 0x6906c2feU, 0xf762575dU, 
0x806567cbU, 0x196c3671U, 0x6e6b06e7U,
+     0xfed41b76U, 0x89d32be0U, 0x10da7a5aU, 0x67dd4accU, 0xf9b9df6fU, 
0x8ebeeff9U, 0x17b7be43U, 0x60b08ed5U,
+     0xd6d6a3e8U, 0xa1d1937eU, 0x38d8c2c4U, 0x4fdff252U, 0xd1bb67f1U, 
0xa6bc5767U, 0x3fb506ddU, 0x48b2364bU,
+     0xd80d2bdaU, 0xaf0a1b4cU, 0x36034af6U, 0x41047a60U, 0xdf60efc3U, 
0xa867df55U, 0x316e8eefU, 0x4669be79U,
+     0xcb61b38cU, 0xbc66831aU, 0x256fd2a0U, 0x5268e236U, 0xcc0c7795U, 
0xbb0b4703U, 0x220216b9U, 0x5505262fU,
+     0xc5ba3bbeU, 0xb2bd0b28U, 0x2bb45a92U, 0x5cb36a04U, 0xc2d7ffa7U, 
0xb5d0cf31U, 0x2cd99e8bU, 0x5bdeae1dU,
+     0x9b64c2b0U, 0xec63f226U, 0x756aa39cU, 0x026d930aU, 0x9c0906a9U, 
0xeb0e363fU, 0x72076785U, 0x05005713U,
+     0x95bf4a82U, 0xe2b87a14U, 0x7bb12baeU, 0x0cb61b38U, 0x92d28e9bU, 
0xe5d5be0dU, 0x7cdcefb7U, 0x0bdbdf21U,
+     0x86d3d2d4U, 0xf1d4e242U, 0x68ddb3f8U, 0x1fda836eU, 0x81be16cdU, 
0xf6b9265bU, 0x6fb077e1U, 0x18b74777U,
+     0x88085ae6U, 0xff0f6a70U, 0x66063bcaU, 0x11010b5cU, 0x8f659effU, 
0xf862ae69U, 0x616bffd3U, 0x166ccf45U,
+     0xa00ae278U, 0xd70dd2eeU, 0x4e048354U, 0x3903b3c2U, 0xa7672661U, 
0xd06016f7U, 0x4969474dU, 0x3e6e77dbU,
+     0xaed16a4aU, 0xd9d65adcU, 0x40df0b66U, 0x37d83bf0U, 0xa9bcae53U, 
0xdebb9ec5U, 0x47b2cf7fU, 0x30b5ffe9U,
+     0xbdbdf21cU, 0xcabac28aU, 0x53b39330U, 0x24b4a3a6U, 0xbad03605U, 
0xcdd70693U, 0x54de5729U, 0x23d967bfU,
+     0xb3667a2eU, 0xc4614ab8U, 0x5d681b02U, 0x2a6f2b94U, 0xb40bbe37U, 
0xc30c8ea1U, 0x5a05df1bU, 0x2d02ef8dU
+     ];
+
+    defvar c = crc as uint<32>;
+    for (x in buf)
+      {
+       c = table[(c ^ x) & 0xff] ^ (c .>> 8);
+      }
+    return c;
+   }
+
+   return update (0xffffffffU, buf) ^ 0xffffffffU;
+  }
+
+
 /*** Miscellanea.  */
 
 defvar NULL = 0#B;
-- 
2.11.0




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