diff options
author | Abseil Team <absl-team@google.com> | 2023-06-12 13:43:18 -0700 |
---|---|---|
committer | Copybara-Service <copybara-worker@google.com> | 2023-06-12 13:44:03 -0700 |
commit | dfc7f46d9c8425933ffe2c275f982f956d33d06f (patch) | |
tree | e785f6dfb3272b38c241ada5b79b934d3eb12427 /absl/crc/internal/crc.cc | |
parent | 0af0103d3454d312b19d928255996a192df45ec7 (diff) |
Removes unused methods CRC::Empty() and CRC::Concat() from the internal
implementation.
PiperOrigin-RevId: 539749773
Change-Id: Iec83431ffd360a077b153cea00427580ae287d1f
Diffstat (limited to 'absl/crc/internal/crc.cc')
-rw-r--r-- | absl/crc/internal/crc.cc | 31 |
1 files changed, 0 insertions, 31 deletions
diff --git a/absl/crc/internal/crc.cc b/absl/crc/internal/crc.cc index ba4c6d13..22e91c53 100644 --- a/absl/crc/internal/crc.cc +++ b/absl/crc/internal/crc.cc @@ -176,9 +176,6 @@ CRCImpl* CRCImpl::NewInternal() { return result; } -// The CRC of the empty string is always the CRC polynomial itself. -void CRCImpl::Empty(uint32_t* crc) const { *crc = kCrc32cPoly; } - // The 32-bit implementation void CRC32::InitTables() { @@ -435,34 +432,6 @@ CRC* CRC::Crc32c() { return singleton; } -// This Concat implementation works for arbitrary polynomials. -void CRC::Concat(uint32_t* px, uint32_t y, size_t ylen) { - // https://en.wikipedia.org/wiki/Mathematics_of_cyclic_redundancy_checks - // The CRC of a message M is the remainder of polynomial division modulo G, - // where the coefficient arithmetic is performed modulo 2 (so +/- are XOR): - // R(x) = M(x) x**n (mod G) - // (n is the degree of G) - // In practice, we use an initial value A and a bitmask B to get - // R = (A ^ B)x**|M| ^ Mx**n ^ B (mod G) - // If M is the concatenation of two strings S and T, and Z is the string of - // len(T) 0s, then the remainder CRC(ST) can be expressed as: - // R = (A ^ B)x**|ST| ^ STx**n ^ B - // = (A ^ B)x**|SZ| ^ SZx**n ^ B ^ Tx**n - // = CRC(SZ) ^ Tx**n - // CRC(Z) = (A ^ B)x**|T| ^ B - // CRC(T) = (A ^ B)x**|T| ^ Tx**n ^ B - // So R = CRC(SZ) ^ CRC(Z) ^ CRC(T) - // - // And further, since CRC(SZ) = Extend(CRC(S), Z), - // CRC(SZ) ^ CRC(Z) = Extend(CRC(S) ^ CRC(''), Z). - uint32_t z; - uint32_t t; - Empty(&z); - t = *px ^ z; - ExtendByZeroes(&t, ylen); - *px = t ^ y; -} - } // namespace crc_internal ABSL_NAMESPACE_END } // namespace absl |