Miscellaneous C++20 fixups and nits + import latest BCHN HexStr() impl

- Added header src/bitcoin/concepts.h
- Redid some of the templates to better constrain them using concepts
- Imported latest BCHN HexStr() impl. which is slightly faster than what
  we had before.
- Fix prevector const_iterator and iterator to actually conform to
  std::random_access_iterator.

Fulcrum.pro

@@ -452,6 +452,7 @@ HEADERS += \
     bitcoin/block.h \
     bitcoin/cashaddr.h \
     bitcoin/cashaddrenc.h \
+    bitcoin/concepts.h \
     bitcoin/compat.h \
     bitcoin/crypto/byteswap.h \
     bitcoin/crypto/endian.h \

src/bitcoin/concepts.h

@@ -0,0 +1,32 @@
+//
+// Fulcrum - A fast & nimble SPV Server for Bitcoin Cash
+// Copyright (C) 2019-2024 Calin A. Culianu <[email protected]>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program (see LICENSE.txt).  If not, see
+// <https://www.gnu.org/licenses/>.
+//
+#pragma once
+
+#include <cstddef> // for std::byte
+#include <cstdint>
+#include <type_traits>
+
+namespace bitcoin {
+
+// Added by Calin to make some of the bitcoin code more generic
+template <typename T>
+concept ByteLike = std::is_same_v<T, char> || std::is_same_v<T, uint8_t> || std::is_same_v<T, std::byte>
+                   || std::is_same_v<T, int8_t> || std::is_same_v<T, signed char> || std::is_same_v<T, unsigned char>;
+
+} // namespace bitcoin

src/bitcoin/hash.h

@@ -5,16 +5,15 @@
 
 #pragma once
 
+#include "Span.h"
+
+#include "concepts.h"
 #include "crypto/ripemd160.h"
 #include "crypto/sha256.h"
 #include "uint256.h"
 #include "version.h"
 #include "serialize.h"
 
-#include <cstddef> // for std::byte
-#include <type_traits>
-#include <vector>
-
 #ifdef __clang__
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wold-style-cast"
@@ -25,10 +24,6 @@ namespace bitcoin {
 
 using ChainCode = uint256;
 
-// Added by Calin to make some of the bitcoin code below more generic
-template <typename T>
-concept ByteLike = std::is_same_v<T, char> || std::is_same_v<T, uint8_t> || std::is_same_v<T, std::byte>;
-
 /** A hasher class for Bitcoin's 256-bit hash (double SHA-256). */
 class CHash256 {
 private:
@@ -90,7 +85,8 @@ class CHash160 {
 };
 
 /** Compute the 256-bit hash of an object. */
-template <typename T1> inline uint256 Hash(const T1 pbegin, const T1 pend, bool once = false) {
+template <std::random_access_iterator T1>
+inline uint256 Hash(const T1 pbegin, const T1 pend, bool once = false) {
     const uint8_t pblank[1] = {};
     uint256 result{uint256::Uninitialized};
     CHash256(once)
@@ -101,17 +97,17 @@ template <typename T1> inline uint256 Hash(const T1 pbegin, const T1 pend, bool
 }
 
 /** Compute the 256-bit SINGLE hash of an object. This was added by Calin to work with ElectrumX */
-template <typename T1> inline uint256 HashOnce(const T1 pbegin, const T1 pend) {
+template <std::random_access_iterator T1>
+inline uint256 HashOnce(const T1 pbegin, const T1 pend) {
     return Hash(pbegin, pend, true);
 }
 
 inline uint256 Hash(Span<const uint8_t> sp) { return Hash(sp.begin(), sp.end()); }
 inline uint256 HashOnce(Span<const uint8_t> sp) { return Hash(sp.begin(), sp.end(), true); }
 
 /** Compute the 256-bit hash of the concatenation of two objects. */
-template <typename T1, typename T2>
-inline uint256 Hash(const T1 p1begin, const T1 p1end, const T2 p2begin,
-                    const T2 p2end) {
+template <std::random_access_iterator T1, std::random_access_iterator T2>
+inline uint256 Hash(const T1 p1begin, const T1 p1end, const T2 p2begin, const T2 p2end) {
     const uint8_t pblank[1] = {};
     uint256 result{uint256::Uninitialized};
     CHash256()
@@ -124,9 +120,8 @@ inline uint256 Hash(const T1 p1begin, const T1 p1end, const T2 p2begin,
 }
 
 /** Compute the 256-bit hash of the concatenation of three objects. */
-template <typename T1, typename T2, typename T3>
-inline uint256 Hash(const T1 p1begin, const T1 p1end, const T2 p2begin,
-                    const T2 p2end, const T3 p3begin, const T3 p3end) {
+template <std::random_access_iterator T1, std::random_access_iterator T2, std::random_access_iterator T3>
+inline uint256 Hash(const T1 p1begin, const T1 p1end, const T2 p2begin, const T2 p2end, const T3 p3begin, const T3 p3end) {
     const uint8_t pblank[1] = {};
     uint256 result{uint256::Uninitialized};
     CHash256()
@@ -141,7 +136,8 @@ inline uint256 Hash(const T1 p1begin, const T1 p1end, const T2 p2begin,
 }
 
 /** Compute the 160-bit hash an object. */
-template <typename T1> inline uint160 Hash160(const T1 pbegin, const T1 pend) {
+template <std::random_access_iterator T1>
+inline uint160 Hash160(const T1 pbegin, const T1 pend) {
     const uint8_t pblank[1] = {};
     uint160 result{uint160::Uninitialized};
     CHash160()
@@ -187,7 +183,8 @@ class CHashWriter {
     template <ByteLike ByteT>
     void GetHashInPlace(ByteT buf[CHash256::OUTPUT_SIZE]) { ctx.Finalize(buf); }
 
-    template <typename T> CHashWriter &operator<<(const T &obj) {
+    template <typename T>
+    CHashWriter &operator<<(const T &obj) {
         // Serialize to this stream
         bitcoin::Serialize(*this, obj);
         return *this;
@@ -198,14 +195,14 @@ class CHashWriter {
  * Reads data from an underlying stream, while hashing the read data.
  */
 
-template <typename Source> class CHashVerifier : public CHashWriter {
+template <typename Source>
+class CHashVerifier : public CHashWriter {
 private:
     Source *source;
 
 public:
     explicit CHashVerifier(Source *source_)
-        : CHashWriter(source_->GetType(), source_->GetVersion()),
-          source(source_) {}
+        : CHashWriter(source_->GetType(), source_->GetVersion()), source(source_) {}
 
     template <ByteLike ByteT>
     void read(ByteT *pch, size_t nSize) {
@@ -232,8 +229,7 @@ template <typename Source> class CHashVerifier : public CHashWriter {
 /** Compute the 256-bit hash of an object's serialization. */
 
 template <typename T>
-uint256 SerializeHash(const T &obj, int nType = SER_GETHASH,
-                      int nVersion = PROTOCOL_VERSION, bool once = false) {
+uint256 SerializeHash(const T &obj, int nType = SER_GETHASH, int nVersion = PROTOCOL_VERSION, bool once = false) {
     CHashWriter ss(nType, nVersion, once);
     ss << obj;
     return ss.GetHash();
@@ -249,10 +245,9 @@ void SerializeHashInPlace(ByteT hash[CHash256::OUTPUT_SIZE], const T &obj,
 }
 
 // MurmurHash3: ultra-fast hash suitable for hash tables but not cryptographically secure
-uint32_t MurmurHash3(uint32_t nHashSeed,
-                     const uint8_t *pDataToHash, size_t nDataLen /* bytes */);
-inline uint32_t MurmurHash3(uint32_t nHashSeed,
-                            const std::vector<uint8_t> &vDataToHash) {
+uint32_t MurmurHash3(uint32_t nHashSeed, const uint8_t *pDataToHash, size_t nDataLen /* bytes */);
+
+inline uint32_t MurmurHash3(uint32_t nHashSeed, Span<const uint8_t> vDataToHash) {
     return MurmurHash3(nHashSeed, vDataToHash.data(), vDataToHash.size());
 }
 

src/bitcoin/prevector.h

@@ -82,15 +82,16 @@ class prevector {
             return iterator(ptr--);
         }
         difference_type friend operator-(iterator a, iterator b) {
-            return &*a - &*b;
+            return a.ptr - b.ptr;
         }
-        iterator operator+(size_type n) { return iterator(ptr + n); }
-        iterator &operator+=(size_type n) {
+        iterator operator+(difference_type n) const { return iterator(ptr + n); }
+        friend iterator operator+(difference_type n, iterator b) { return iterator(b.ptr + n); }
+        iterator &operator+=(difference_type n) {
             ptr += n;
             return *this;
         }
-        iterator operator-(size_type n) { return iterator(ptr - n); }
-        iterator &operator-=(size_type n) {
+        iterator operator-(difference_type n) const { return iterator(ptr - n); }
+        iterator &operator-=(difference_type n) {
             ptr -= n;
             return *this;
         }
@@ -144,7 +145,7 @@ class prevector {
         const_iterator(iterator x) : ptr(&(*x)) {}
         const T &operator*() const { return *ptr; }
         const T *operator->() const { return ptr; }
-        const T &operator[](size_type pos) const { return ptr[pos]; }
+        const T &operator[](difference_type pos) const { return ptr[pos]; }
         const_iterator &operator++() {
             ++ptr;
             return *this;
@@ -160,19 +161,22 @@ class prevector {
             return const_iterator(ptr--);
         }
         difference_type friend operator-(const_iterator a, const_iterator b) {
-            return &*a - &*b;
+            return a.ptr - b.ptr;
         }
-        const_iterator operator+(size_type n) {
+        const_iterator operator+(difference_type n) const {
             return const_iterator(ptr + n);
         }
-        const_iterator &operator+=(size_type n) {
+        friend const_iterator operator+(difference_type n, const_iterator b) {
+            return const_iterator(b.ptr + n);
+        }
+        const_iterator &operator+=(difference_type n) {
             ptr += n;
             return *this;
         }
-        const_iterator operator-(size_type n) {
+        const_iterator operator-(difference_type n) const {
             return const_iterator(ptr - n);
         }
-        const_iterator &operator-=(size_type n) {
+        const_iterator &operator-=(difference_type n) {
             ptr -= n;
             return *this;
         }

src/bitcoin/utilstrencodings.cpp

@@ -23,6 +23,17 @@
 
 namespace bitcoin {
 
+namespace strencodings {
+// used by the HexStr template function as a lookup table to convert bytes -> hex
+const char hexmap[513] =
+    "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f"
+    "303132333435363738393a3b3c3d3e3f404142434445464748494a4b4c4d4e4f505152535455565758595a5b5c5d5e5f"
+    "606162636465666768696a6b6c6d6e6f707172737475767778797a7b7c7d7e7f808182838485868788898a8b8c8d8e8f"
+    "909192939495969798999a9b9c9d9e9fa0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebf"
+    "c0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedfe0e1e2e3e4e5e6e7e8e9eaebecedeeef"
+    "f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff";
+} // namespace strencodings
+
 static const std::string CHARS_ALPHA_NUM =
     "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 
@@ -45,7 +56,7 @@ std::string SanitizeString(const std::string &str, int rule) {
     return strResult;
 }
 
-const signed char p_util_hexdigit[256] = {
+static const signed char p_util_hexdigit[256] = {
     -1, -1,  -1,  -1,  -1,  -1,  -1,  -1, -1, -1, -1, -1, -1, -1, -1, -1,
     -1, -1,  -1,  -1,  -1,  -1,  -1,  -1, -1, -1, -1, -1, -1, -1, -1, -1,
     -1, -1,  -1,  -1,  -1,  -1,  -1,  -1, -1, -1, -1, -1, -1, -1, -1, -1,

src/bitcoin/utilstrencodings.h

@@ -8,7 +8,13 @@
  */
 #pragma once
 
+#include "concepts.h"
+#include "Span.h"
+
+#include <cassert>
+#include <cstddef>
 #include <cstdint>
+#include <iterator>
 #include <string>
 #include <vector>
 
@@ -116,25 +122,66 @@ bool ParseUInt64(const std::string &str, uint64_t *out);
  */
 bool ParseDouble(const std::string &str, double *out);
 
-template <typename T>
+namespace strencodings {
+// We use a hex lookup table with a series of hex pairs all in 1 string in order to ensure locality of reference.
+// This is indexed as hexmap[ubyte_val * 2].
+extern const char hexmap[513];
+} // namespace strencodings
+
+template <std::random_access_iterator T>
+requires (ByteLike<std::iter_value_t<T>>)
 std::string HexStr(const T itbegin, const T itend, bool fSpaces = false) {
     std::string rv;
-    static const char hexmap[16] = {'0', '1', '2', '3', '4', '5', '6', '7',
-                                    '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
-    rv.reserve((itend - itbegin) * 3);
-    for (T it = itbegin; it < itend; ++it) {
-        uint8_t val = uint8_t(*it);
-        if (fSpaces && it != itbegin) rv.push_back(' ');
-        rv.push_back(hexmap[val >> 4]);
-        rv.push_back(hexmap[val & 0xfu]);
+    using strencodings::hexmap;
+    using diff_t = std::iter_difference_t<T>;
+    const diff_t iSpaces = diff_t(fSpaces);
+    diff_t size = (itend - itbegin) * (2 + iSpaces);
+    if (size <= 0) // short-circuit return and/or guard against invalid usage
+        return rv;
+    size -= iSpaces;  // fSpaces only: deduct 1 space for first item
+    rv.resize(static_cast<size_t>(size)); // pre-allocate the entire array to avoid using the slower push_back
+    size_t pos = 0;
+    if (!fSpaces) {
+        // this branch is the most likely branch in this codebase
+        for (T it = itbegin; it < itend; ++it) {
+            const char *hex = &hexmap[static_cast<uint8_t>(*it) * 2u];
+            rv[pos++] = *hex++;
+            rv[pos++] = *hex;
+        }
+    } else {
+        // we unroll the first iteration (which prints no space) to avoid any branching while looping
+        T it = itbegin;
+        if (it < itend) {
+            // first iteration, no space
+            const char *hex = &hexmap[static_cast<uint8_t>(*it) * 2u];
+            rv[pos++] = *hex++;
+            rv[pos++] = *hex;
+            ++it;
+            for (; it < itend; ++it) {
+                // subsequent iterations (if any), unconditionally prepend space
+                rv[pos++] = ' ';
+                hex = &hexmap[static_cast<uint8_t>(*it) * 2u];
+                rv[pos++] = *hex++;
+                rv[pos++] = *hex;
+            }
+        }
     }
+    assert(pos == rv.size());
 
     return rv;
 }
 
-template <typename T>
-inline std::string HexStr(const T &vch, bool fSpaces = false) {
-    return HexStr(vch.begin(), vch.end(), fSpaces);
+/**
+ * Convert a span of bytes to a lower-case hexadecimal string.
+ */
+inline std::string HexStr(const Span<const uint8_t> input, bool fSpaces = false) {
+    return HexStr(input.begin(), input.end(), fSpaces);
+}
+inline std::string HexStr(const Span<const char> input, bool fSpaces = false) {
+    return HexStr(MakeUInt8Span(input), fSpaces);
+}
+inline std::string HexStr(const Span<const std::byte> input, bool fSpaces = false) {
+    return HexStr(MakeUInt8Span(input), fSpaces);
 }
 
 /**