From e1d76bdc4265d37a694d23457881ffdacf0177a4 Mon Sep 17 00:00:00 2001
From: DualFroz <me@dualfroz.com>
Date: Sun, 23 Aug 2026 11:55:36 +0200
Subject: [PATCH] feat(core): implement varint and byte-buffer codec utilities

---
 core/src/Codec.cpp | 469 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 469 insertions(+)
 create mode 100644 core/src/Codec.cpp

diff --git a/core/src/Codec.cpp b/core/src/Codec.cpp
new file mode 100644
index 0000000..a03213b
--- /dev/null
+++ b/core/src/Codec.cpp
@@ -0,0 +1,469 @@
+#include "vf/Codec.h"
+
+#include <cstring>
+
+namespace vf {
+
+void ByteWriter::putU16(uint16_t v) {
+    buffer.push_back(static_cast<uint8_t>((v >> 8) & 0xFFu));
+    buffer.push_back(static_cast<uint8_t>(v & 0xFFu));
+}
+
+void ByteWriter::putU32(uint32_t v) {
+    for (int shift = 24; shift >= 0; shift -= 8)
+        buffer.push_back(static_cast<uint8_t>((v >> shift) & 0xFFu));
+}
+
+void ByteWriter::putU64(uint64_t v) {
+    for (int shift = 56; shift >= 0; shift -= 8)
+        buffer.push_back(static_cast<uint8_t>((v >> shift) & 0xFFu));
+}
+
+void ByteWriter::putVarU32(uint32_t v) {
+    while (v >= 0x80u) {
+        buffer.push_back(static_cast<uint8_t>(v) | 0x80u);
+        v >>= 7;
+    }
+    buffer.push_back(static_cast<uint8_t>(v));
+}
+
+void ByteWriter::putVarU64(uint64_t v) {
+    while (v >= 0x80u) {
+        buffer.push_back(static_cast<uint8_t>(v) | 0x80u);
+        v >>= 7;
+    }
+    buffer.push_back(static_cast<uint8_t>(v));
+}
+
+void ByteWriter::putVarI32(int32_t v) { putVarU32(zigzagEncode32(v)); }
+void ByteWriter::putVarI64(int64_t v) { putVarU64(zigzagEncode64(v)); }
+
+void ByteWriter::putFloat(float v) {
+    uint32_t bits;
+    std::memcpy(&bits, &v, sizeof(bits));
+    putU32(bits);
+}
+
+void ByteWriter::putDouble(double v) {
+    uint64_t bits;
+    std::memcpy(&bits, &v, sizeof(bits));
+    putU64(bits);
+}
+
+void ByteWriter::putBytes(const uint8_t* p, std::size_t n) {
+    buffer.insert(buffer.end(), p, p + n);
+}
+
+void ByteWriter::putString(const std::string& s) {
+    putVarU32(static_cast<uint32_t>(s.size()));
+    buffer.insert(buffer.end(), s.begin(), s.end());
+}
+
+bool ByteReader::need(std::size_t n) {
+    if (failed || cursor + n > size) {
+        failed = true;
+        return false;
+    }
+    return true;
+}
+
+bool ByteReader::getU8(uint8_t& out) {
+    if (!need(1)) return false;
+    out = data[cursor++];
+    return true;
+}
+
+bool ByteReader::getU16(uint16_t& out) {
+    if (!need(2)) return false;
+    out = static_cast<uint16_t>((data[cursor] << 8) | data[cursor + 1]);
+    cursor += 2;
+    return true;
+}
+
+bool ByteReader::getU32(uint32_t& out) {
+    if (!need(4)) return false;
+    out = 0;
+    for (int i = 0; i < 4; ++i) out = (out << 8) | data[cursor + static_cast<std::size_t>(i)];
+    cursor += 4;
+    return true;
+}
+
+bool ByteReader::getU64(uint64_t& out) {
+    if (!need(8)) return false;
+    out = 0;
+    for (int i = 0; i < 8; ++i) out = (out << 8) | data[cursor + static_cast<std::size_t>(i)];
+    cursor += 8;
+    return true;
+}
+
+bool ByteReader::getVarU32(uint32_t& out) {
+    out = 0;
+    for (int shift = 0; shift < 35; shift += 7) {
+        uint8_t byte;
+        if (!getU8(byte)) return false;
+        out |= static_cast<uint32_t>(byte & 0x7Fu) << shift;
+        if ((byte & 0x80u) == 0) return true;
+    }
+    failed = true;
+    return false;
+}
+
+bool ByteReader::getVarU64(uint64_t& out) {
+    out = 0;
+    for (int shift = 0; shift < 70; shift += 7) {
+        uint8_t byte;
+        if (!getU8(byte)) return false;
+        out |= static_cast<uint64_t>(byte & 0x7Fu) << shift;
+        if ((byte & 0x80u) == 0) return true;
+    }
+    failed = true;
+    return false;
+}
+
+bool ByteReader::getVarI32(int32_t& out) {
+    uint32_t raw;
+    if (!getVarU32(raw)) return false;
+    out = zigzagDecode32(raw);
+    return true;
+}
+
+bool ByteReader::getVarI64(int64_t& out) {
+    uint64_t raw;
+    if (!getVarU64(raw)) return false;
+    out = zigzagDecode64(raw);
+    return true;
+}
+
+bool ByteReader::getFloat(float& out) {
+    uint32_t bits;
+    if (!getU32(bits)) return false;
+    std::memcpy(&out, &bits, sizeof(out));
+    return true;
+}
+
+bool ByteReader::getDouble(double& out) {
+    uint64_t bits;
+    if (!getU64(bits)) return false;
+    std::memcpy(&out, &bits, sizeof(out));
+    return true;
+}
+
+bool ByteReader::getBytes(uint8_t* dst, std::size_t n) {
+    if (!need(n)) return false;
+    std::memcpy(dst, data + cursor, n);
+    cursor += n;
+    return true;
+}
+
+bool ByteReader::getString(std::string& out) {
+    uint32_t len;
+    if (!getVarU32(len)) return false;
+    if (!need(len)) return false;
+    out.assign(reinterpret_cast<const char*>(data + cursor), len);
+    cursor += len;
+    return true;
+}
+
+uint32_t zigzagEncode32(int32_t v) {
+    return (static_cast<uint32_t>(v) << 1) ^ static_cast<uint32_t>(v >> 31);
+}
+
+int32_t zigzagDecode32(uint32_t v) {
+    return static_cast<int32_t>((v >> 1) ^ (0u - (v & 1u)));
+}
+
+uint64_t zigzagEncode64(int64_t v) {
+    return (static_cast<uint64_t>(v) << 1) ^ static_cast<uint64_t>(v >> 63);
+}
+
+int64_t zigzagDecode64(uint64_t v) {
+    return static_cast<int64_t>((v >> 1) ^ (0ull - (v & 1ull)));
+}
+
+uint32_t fnv1a32(const uint8_t* data, std::size_t size) {
+    uint32_t h = 2166136261u;
+    for (std::size_t i = 0; i < size; ++i) {
+        h ^= data[i];
+        h *= 16777619u;
+    }
+    return h;
+}
+
+uint64_t fnv1a64(const uint8_t* data, std::size_t size) {
+    uint64_t h = 1469598103934665603ull;
+    for (std::size_t i = 0; i < size; ++i) {
+        h ^= data[i];
+        h *= 1099511628211ull;
+    }
+    return h;
+}
+
+uint32_t adler32(const uint8_t* data, std::size_t size) {
+    const uint32_t modulo = 65521u;
+    uint32_t a = 1, b = 0;
+    for (std::size_t i = 0; i < size; ++i) {
+        a = (a + data[i]) % modulo;
+        b = (b + a) % modulo;
+    }
+    return (b << 16) | a;
+}
+
+namespace {
+
+constexpr uint8_t rleRunFlag = 0x80;
+constexpr int rleMinRun = 3;
+constexpr int rleMaxRun = 130;
+constexpr int rleMaxLiteral = 128;
+
+}  // namespace
+
+ByteBuffer rleEncode(const uint8_t* data, std::size_t size) {
+    ByteBuffer out;
+    std::size_t i = 0;
+    while (i < size) {
+        std::size_t runEnd = i + 1;
+        while (runEnd < size && data[runEnd] == data[i] &&
+               runEnd - i < static_cast<std::size_t>(rleMaxRun))
+            ++runEnd;
+        std::size_t runLen = runEnd - i;
+        if (runLen >= static_cast<std::size_t>(rleMinRun)) {
+            out.push_back(static_cast<uint8_t>(rleRunFlag | (runLen - rleMinRun)));
+            out.push_back(data[i]);
+            i = runEnd;
+            continue;
+        }
+        std::size_t litStart = i;
+        while (i < size) {
+            std::size_t look = i + 1;
+            while (look < size && data[look] == data[i] &&
+                   look - i < static_cast<std::size_t>(rleMinRun))
+                ++look;
+            if (look - i >= static_cast<std::size_t>(rleMinRun)) break;
+            ++i;
+            if (i - litStart == static_cast<std::size_t>(rleMaxLiteral)) break;
+        }
+        std::size_t litLen = i - litStart;
+        out.push_back(static_cast<uint8_t>(litLen - 1));
+        out.insert(out.end(), data + litStart, data + i);
+    }
+    return out;
+}
+
+bool rleDecode(const uint8_t* data, std::size_t size, ByteBuffer& out) {
+    out.clear();
+    std::size_t i = 0;
+    while (i < size) {
+        uint8_t control = data[i++];
+        if (control & rleRunFlag) {
+            std::size_t runLen = static_cast<std::size_t>(control & 0x7Fu) + rleMinRun;
+            if (i >= size) return false;
+            uint8_t value = data[i++];
+            out.insert(out.end(), runLen, value);
+        } else {
+            std::size_t litLen = static_cast<std::size_t>(control) + 1;
+            if (i + litLen > size) return false;
+            out.insert(out.end(), data + i, data + i + litLen);
+            i += litLen;
+        }
+    }
+    return true;
+}
+
+namespace {
+
+constexpr int lzMinMatch = 4;
+constexpr int lzHashBits = 15;
+constexpr int lzHashSize = 1 << lzHashBits;
+constexpr int lzMaxChain = 128;
+constexpr uint32_t lzMaxOffset = 1u << 20;
+
+uint32_t hash4(const uint8_t* p) {
+    uint32_t v;
+    std::memcpy(&v, p, sizeof(v));
+    return (v * 2654435761u) >> (32 - lzHashBits);
+}
+
+void putVarU32Raw(ByteBuffer& out, uint32_t v) {
+    while (v >= 0x80u) {
+        out.push_back(static_cast<uint8_t>(v) | 0x80u);
+        v >>= 7;
+    }
+    out.push_back(static_cast<uint8_t>(v));
+}
+
+bool getVarU32Raw(const uint8_t* data, std::size_t size, std::size_t& pos, uint32_t& out) {
+    out = 0;
+    for (int shift = 0; shift < 35; shift += 7) {
+        if (pos >= size) return false;
+        uint8_t byte = data[pos++];
+        out |= static_cast<uint32_t>(byte & 0x7Fu) << shift;
+        if ((byte & 0x80u) == 0) return true;
+    }
+    return false;
+}
+
+}  // namespace
+
+ByteBuffer lz77Compress(const uint8_t* data, std::size_t size) {
+    ByteBuffer out;
+    putVarU32Raw(out, static_cast<uint32_t>(size));
+    if (size == 0) return out;
+
+    std::vector<int32_t> head(lzHashSize, -1);
+    std::vector<int32_t> prev(size, -1);
+
+    std::size_t pos = 0;
+    std::size_t flagIndex = out.size();
+    out.push_back(0);
+    int flagBit = 0;
+
+    auto insert = [&](std::size_t at) {
+        if (at + lzMinMatch <= size) {
+            uint32_t h = hash4(data + at);
+            prev[at] = head[h];
+            head[h] = static_cast<int32_t>(at);
+        }
+    };
+
+    while (pos < size) {
+        std::size_t bestLen = 0;
+        std::size_t bestOffset = 0;
+        if (pos + lzMinMatch <= size) {
+            uint32_t h = hash4(data + pos);
+            int32_t candidate = head[h];
+            int chain = 0;
+            std::size_t maxLen = size - pos;
+            while (candidate >= 0 && chain < lzMaxChain) {
+                std::size_t cand = static_cast<std::size_t>(candidate);
+                if (pos - cand > lzMaxOffset) break;
+                std::size_t len = 0;
+                while (len < maxLen && data[cand + len] == data[pos + len]) ++len;
+                if (len > bestLen) {
+                    bestLen = len;
+                    bestOffset = pos - cand;
+                    if (len == maxLen) break;
+                }
+                candidate = prev[cand];
+                ++chain;
+            }
+        }
+
+        if (bestLen >= static_cast<std::size_t>(lzMinMatch)) {
+            out[flagIndex] = static_cast<uint8_t>(out[flagIndex] | (1u << flagBit));
+            putVarU32Raw(out, static_cast<uint32_t>(bestOffset));
+            putVarU32Raw(out, static_cast<uint32_t>(bestLen - lzMinMatch));
+            std::size_t end = pos + bestLen;
+            while (pos < end) {
+                insert(pos);
+                ++pos;
+            }
+        } else {
+            out.push_back(data[pos]);
+            insert(pos);
+            ++pos;
+        }
+
+        if (++flagBit == 8) {
+            flagBit = 0;
+            if (pos < size) {
+                flagIndex = out.size();
+                out.push_back(0);
+            }
+        }
+    }
+    return out;
+}
+
+bool lz77Decompress(const uint8_t* data, std::size_t size, ByteBuffer& out) {
+    out.clear();
+    std::size_t pos = 0;
+    uint32_t rawLen;
+    if (!getVarU32Raw(data, size, pos, rawLen)) return false;
+    out.reserve(rawLen);
+
+    while (out.size() < rawLen) {
+        if (pos >= size) return false;
+        uint8_t flag = data[pos++];
+        for (int bit = 0; bit < 8 && out.size() < rawLen; ++bit) {
+            if (flag & (1u << bit)) {
+                uint32_t offset, extra;
+                if (!getVarU32Raw(data, size, pos, offset)) return false;
+                if (!getVarU32Raw(data, size, pos, extra)) return false;
+                std::size_t len = static_cast<std::size_t>(extra) + lzMinMatch;
+                if (offset == 0 || offset > out.size()) return false;
+                if (out.size() + len > rawLen) return false;
+                std::size_t from = out.size() - offset;
+                for (std::size_t i = 0; i < len; ++i) out.push_back(out[from + i]);
+            } else {
+                if (pos >= size) return false;
+                out.push_back(data[pos++]);
+            }
+        }
+    }
+    return out.size() == rawLen;
+}
+
+ByteBuffer compress(const uint8_t* data, std::size_t size) {
+    ByteBuffer rle = rleEncode(data, size);
+    ByteBuffer lz = lz77Compress(data, size);
+
+    CodecMethod method = CodecMethod::Store;
+    const ByteBuffer* payload = nullptr;
+    std::size_t best = size;
+    if (rle.size() < best) {
+        best = rle.size();
+        method = CodecMethod::Rle;
+        payload = &rle;
+    }
+    if (lz.size() < best) {
+        method = CodecMethod::Lz77;
+        payload = &lz;
+    }
+
+    ByteWriter head;
+    head.putU8(static_cast<uint8_t>(method));
+    head.putVarU32(static_cast<uint32_t>(size));
+    head.putU32(fnv1a32(data, size));
+
+    ByteBuffer out = head.bytes();
+    if (method == CodecMethod::Store)
+        out.insert(out.end(), data, data + size);
+    else
+        out.insert(out.end(), payload->begin(), payload->end());
+    return out;
+}
+
+ByteBuffer compress(const ByteBuffer& in) { return compress(in.data(), in.size()); }
+
+bool decompress(const uint8_t* data, std::size_t size, ByteBuffer& out) {
+    ByteReader reader(data, size);
+    uint8_t rawMethod;
+    uint32_t rawLen;
+    uint32_t checksum;
+    if (!reader.getU8(rawMethod)) return false;
+    if (!reader.getVarU32(rawLen)) return false;
+    if (!reader.getU32(checksum)) return false;
+
+    const uint8_t* payload = data + reader.position();
+    std::size_t payloadSize = reader.remaining();
+
+    switch (static_cast<CodecMethod>(rawMethod)) {
+        case CodecMethod::Store:
+            if (payloadSize != rawLen) return false;
+            out.assign(payload, payload + payloadSize);
+            break;
+        case CodecMethod::Rle:
+            if (!rleDecode(payload, payloadSize, out)) return false;
+            break;
+        case CodecMethod::Lz77:
+            if (!lz77Decompress(payload, payloadSize, out)) return false;
+            break;
+        default:
+            return false;
+    }
+
+    if (out.size() != rawLen) return false;
+    return fnv1a32(out.data(), out.size()) == checksum;
+}
+
+} // namespace vf