summaryrefslogtreecommitdiff
path: root/absl/crc
diff options
context:
space:
mode:
authorGravatar Abseil Team <absl-team@google.com>2023-06-12 13:43:18 -0700
committerGravatar Copybara-Service <copybara-worker@google.com>2023-06-12 13:44:03 -0700
commitdfc7f46d9c8425933ffe2c275f982f956d33d06f (patch)
treee785f6dfb3272b38c241ada5b79b934d3eb12427 /absl/crc
parent0af0103d3454d312b19d928255996a192df45ec7 (diff)
Removes unused methods CRC::Empty() and CRC::Concat() from the internal
implementation. PiperOrigin-RevId: 539749773 Change-Id: Iec83431ffd360a077b153cea00427580ae287d1f
Diffstat (limited to 'absl/crc')
-rw-r--r--absl/crc/internal/crc.cc31
-rw-r--r--absl/crc/internal/crc.h8
-rw-r--r--absl/crc/internal/crc_internal.h2
3 files changed, 0 insertions, 41 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
diff --git a/absl/crc/internal/crc.h b/absl/crc/internal/crc.h
index e683c25f..4efdd032 100644
--- a/absl/crc/internal/crc.h
+++ b/absl/crc/internal/crc.h
@@ -40,9 +40,6 @@ class CRC {
public:
virtual ~CRC();
- // Place the CRC of the empty string in "*crc"
- virtual void Empty(uint32_t* crc) const = 0;
-
// If "*crc" is the CRC of bytestring A, place the CRC of
// the bytestring formed from the concatenation of A and the "length"
// bytes at "bytes" into "*crc".
@@ -58,11 +55,6 @@ class CRC {
// with those zero bytes removed.
virtual void UnextendByZeroes(uint32_t* crc, size_t length) const = 0;
- // If *px is the CRC (as defined by *crc) of some string X,
- // and y is the CRC of some string Y that is ylen bytes long, set
- // *px to the CRC of the concatenation of X followed by Y.
- virtual void Concat(uint32_t* px, uint32_t y, size_t ylen);
-
// Apply a non-linear transformation to "*crc" so that
// it is safe to CRC the result with the same polynomial without
// any reduction of error-detection ability in the outer CRC.
diff --git a/absl/crc/internal/crc_internal.h b/absl/crc/internal/crc_internal.h
index 7d77bdf5..4d3582d9 100644
--- a/absl/crc/internal/crc_internal.h
+++ b/absl/crc/internal/crc_internal.h
@@ -70,8 +70,6 @@ class CRCImpl : public CRC { // Implementation of the abstract class CRC
// The internal version of CRC::New().
static CRCImpl* NewInternal();
- void Empty(uint32_t* crc) const override;
-
// Fill in a table for updating a CRC by one word of 'word_size' bytes
// [last_lo, last_hi] contains the answer if the last bit in the word
// is set.