commit 36c026d26bc26904e7a488859e0b5aba4020fded
Author: Dnomd343 <dnomd343@gmail.com>
Date:   Thu Mar 14 22:16:02 2024 +0800

    feat: md5 algorithm of blocks

diff --git a/main.cc b/main.cc
new file mode 100644
index 0000000..c443927
--- /dev/null
+++ b/main.cc
@@ -0,0 +1,35 @@
+#include <iostream>
+
+#include "md5_core.h"
+
+std::string test_data() {
+    char data[64];
+    for (char i = 0; i < 64; ++i) {
+        data[i] = i;
+    }
+    return {data, data + 64};
+}
+
+void dump_ctx(const md5::md5_ctx *c) {
+    std::cout << std::hex << c->A << std::endl;
+    std::cout << std::hex << c->B << std::endl;
+    std::cout << std::hex << c->C << std::endl;
+    std::cout << std::hex << c->D << std::endl;
+    std::cout << std::dec << c->size << std::endl;
+}
+
+int main() {
+    auto data = test_data() + test_data() + test_data() + test_data();
+
+    md5::md5_ctx c;
+    dump_ctx(&c);
+
+    md5::md5_process(&c, data.c_str(), data.size());
+    md5::md5_process(&c, data.c_str(), data.size());
+    dump_ctx(&c);
+
+    md5::md5_reset(&c);
+    md5::md5_process(&c, data.c_str(), data.size());
+    md5::md5_process(&c, data.c_str(), data.size());
+    dump_ctx(&c);
+}
diff --git a/md5_core.cc b/md5_core.cc
new file mode 100644
index 0000000..40d780e
--- /dev/null
+++ b/md5_core.cc
@@ -0,0 +1,102 @@
+#include "md5_core.h"
+#include "md5_math.h"
+
+#define RA A, B, C, D
+#define RB D, A, B, C
+#define RC C, D, A, B
+#define RD B, C, D, A
+
+#define F(x, y, z) (z ^ (x & (y ^ z)))
+#define G(x, y, z) (y ^ (z & (x ^ y)))
+#define H(x, y, z) (x ^ y ^ z)
+#define I(x, y, z) (y ^ (x | ~z))
+
+#define CYCLIC(w, s) (w = (w << s) | (w >> (32 - s)))
+
+#define STEP(i, f, a, b, c, d)               \
+    do {                                     \
+        a += f(b, c, d) + data[K(i)] + T(i); \
+        CYCLIC(a, S(i));                     \
+        a += b;                              \
+    } while (0)
+
+#define FF(i, ...) STEP((0x00 | i), F, __VA_ARGS__)
+#define GG(i, ...) STEP((0x10 | i), G, __VA_ARGS__)
+#define HH(i, ...) STEP((0x20 | i), H, __VA_ARGS__)
+#define II(i, ...) STEP((0x30 | i), I, __VA_ARGS__)
+
+#define MD5_ROUND(OP) \
+    OP(0x0, RA); OP(0x1, RB); OP(0x2, RC); OP(0x3, RD); \
+    OP(0x4, RA); OP(0x5, RB); OP(0x6, RC); OP(0x7, RD); \
+    OP(0x8, RA); OP(0x9, RB); OP(0xa, RC); OP(0xb, RD); \
+    OP(0xc, RA); OP(0xd, RB); OP(0xe, RC); OP(0xf, RD);
+
+namespace md5 {
+
+consteval int K(int index) {
+    int i = index >> 4;
+    const int step[] = {1, 5, 3, 7};
+    const int begin[] = {0, 1, 5, 0};
+    return (begin[i] + step[i] * index) & 0b1111;
+}
+
+consteval int S(int index) {
+    const int map[][4] = {
+        {7, 12, 17, 22},
+        {5, 9, 14, 20},
+        {4, 11, 16, 23},
+        {6, 10, 15, 21},
+    };
+    return map[index >> 4][index & 0b11];
+}
+
+consteval uint32_t T(int index) {
+    double val = math::sin(index + 1);
+    return uint32_t(std::abs(val) * 0x100000000);
+}
+
+void md5_reset(struct md5_ctx *ctx) {
+    ctx->A = MD5_A;
+    ctx->B = MD5_B;
+    ctx->C = MD5_C;
+    ctx->D = MD5_D;
+    ctx->size = 0;
+}
+
+void md5_process(struct md5_ctx *ctx, const void *buffer, uint64_t len) {
+    const auto *data = (uint32_t *)buffer;
+    const auto *limit = data + (len >> 2);
+
+    uint32_t A = ctx->A;
+    uint32_t B = ctx->B;
+    uint32_t C = ctx->C;
+    uint32_t D = ctx->D;
+
+    while (data < limit) {
+        uint32_t A_ = A;
+        uint32_t B_ = B;
+        uint32_t C_ = C;
+        uint32_t D_ = D;
+
+        MD5_ROUND(FF)
+        MD5_ROUND(GG)
+        MD5_ROUND(HH)
+        MD5_ROUND(II)
+
+        A += A_;
+        B += B_;
+        C += C_;
+        D += D_;
+
+        data += 16; // 512 bits
+    }
+
+    ctx->A = A;
+    ctx->B = B;
+    ctx->C = C;
+    ctx->D = D;
+
+    ctx->size += len; // processed size
+}
+
+} // namespace md5
diff --git a/md5_core.h b/md5_core.h
new file mode 100644
index 0000000..8de27dd
--- /dev/null
+++ b/md5_core.h
@@ -0,0 +1,23 @@
+#pragma once
+
+#include <cstdint>
+
+namespace md5 {
+
+constexpr uint32_t MD5_A = 0x67452301;
+constexpr uint32_t MD5_B = 0xefcdab89;
+constexpr uint32_t MD5_C = 0x98badcfe;
+constexpr uint32_t MD5_D = 0x10325476;
+
+struct md5_ctx {
+    uint32_t A = MD5_A;
+    uint32_t B = MD5_B;
+    uint32_t C = MD5_C;
+    uint32_t D = MD5_D;
+    uint64_t size = 0;
+};
+
+void md5_reset(struct md5_ctx *ctx);
+void md5_process(struct md5_ctx *ctx, const void *buffer, uint64_t len);
+
+} // namespace md5
diff --git a/md5_math.h b/md5_math.h
new file mode 100644
index 0000000..dcc26d9
--- /dev/null
+++ b/md5_math.h
@@ -0,0 +1,50 @@
+#pragma once
+
+#include <cmath>
+
+namespace md5::math {
+
+constexpr double PI = 3.141592653589793238462643L;
+
+consteval double pow(double x, int n) {
+    double res = 1;
+    for (int i = 0; i < n; ++i) {
+        res *= x;
+    }
+    return res;
+}
+
+consteval double factorial(int n) {
+    double res = 1;
+    for (int i = 2 ; i <= n ; ++i) {
+        res *= i;
+    }
+    return res;
+}
+
+/// Calculate sin(x) value with Maclaurin series.
+consteval double sin_core(double x) {
+    double res = x;
+    for (int i = 1; i < 80; ++i) {
+        const int n = i * 2 + 1;
+        const int sign = (i & 1) ? -1 : 1;
+        res += sign * pow(x, n) / factorial(n);
+    }
+    return res;
+}
+
+/// Calculate the sin(x) value in radians.
+consteval double sin(double x) {
+    x = std::fmod(x, 2 * PI); // -2PI < x < 2PI
+
+    if (std::abs(x) > PI) {
+        x -= ((x > 0) ? 2 : -2) * PI; // -PI < x < PI
+    }
+
+    if (std::abs(x) > PI / 2) {
+        x = ((x > 0) ? 1 : -1) * PI - x; // -PI / 2 < x < PI / 2
+    }
+    return sin_core(x);
+}
+
+} // namespace md5::math