Shouldn't the polynomial be 0x1EDC6F41 instead of 0x1EDC6F1
On Saturday, July 11, 2015 at 10:18:15 AM UTC-7 Joe Poirier wrote:
> On Sat, Jul 11, 2015 at 10:25 AM, Akira Hayakawa <ruby...@gmail.com>
> wrote:
>
>> Hi,
>>
>> I am at loss how I can compute crc32c hash value with given seed.
>>
>> Some C libraries including Linux kernel's libcrc32c has API that takes
>> three arguments: seed(uint32), data(void *) and the length(int). So the
>> same design in Go's crc32 library helps users import their C programs to
>> Go. Actually, I need the API.
>>
>> I tried crc32.Update(seed, Castagnoli table, data) but the computed value
>> differs from what I compute with Linux's libcrc32c.
>>
>> I am not expertise in crc32c algorithm but I am just a user. So I think I
>> should ask you how to make the same thing as libcrc32c using Go's crc32
>> library.
>>
>>
>>
>>
>> crc32c uses polynomial 0x1EDC6F1 (reversed 0x82F63B78). So from
> src/hash/example_test.go (replace 0xD5828281 with 0x82F63B78):
>
> package crc32_test
>
> import (
> "fmt"
> "hash/crc32"
> )
>
> func ExampleMakeTable() {
> // In this package, the CRC polynomial is represented in reversed
> notation,
> // or LSB-first representation.
> //
> // LSB-first representation is a hexadecimal number with n bits, in
> which the
> // most significant bit represents the coefficient of x⁰ and the least
> significant
> // bit represents the coefficient of xⁿ⁻¹ (the coefficient for xⁿ is
> implicit).
> //
> // For example, CRC32-Q, as defined by the following polynomial,
> // x³²+ x³¹+ x²⁴+ x²²+ x¹⁶+ x¹⁴+ x⁸+ x⁷+ x⁵+ x³+ x¹+ x⁰
> // has the reversed notation 0b11010101100000101000001010000001, so
> the value
> // that should be passed to MakeTable is 0xD5828281.
> crc32q := crc32.MakeTable(0xD5828281)
> fmt.Printf("%08x\n", crc32.Checksum([]byte("Hello world"), crc32q))
> // Output:
> // 2964d064
> }
>
> See more test examples in src/hash/crc32_test.go
>
> *Note, 0x82F63B78 is exported from src/hash/crc32.go as a constant via
> crc32.Castagnoli
>
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