Cleanup crypto utilities (#2549)

* Consolidate crypto functions into single module

* Migrate rest of code to new crypto module

* Fix name conflict

1 files changed, 603 insertions, 0 deletions

diff --git a/source/core/slang-crypto.cpp b/source/core/slang-crypto.cpp
new file mode 100644
index 000000000..ece7b01e9
--- /dev/null
+++ b/source/core/slang-crypto.cpp
@@ -0,0 +1,603 @@
+/*
+ * MD5 implementation is based on:
+ * http://openwall.info/wiki/people/solar/software/public-domain-source-code/md5
+ * Original file header is at the bottom of this file.
+ * 
+ * SHA1 implementation is based on:
+ * https://github.com/983/SHA1
+ * Original LICENSE is at the bottom of this file.
+ */
+
+#include "slang-crypto.h"
+#include "../core/slang-char-util.h"
+
+namespace Slang
+{
+
+// DigestUtil
+
+/*static*/ String DigestUtil::digestToString(const void* digest, SlangInt digestSize)
+{
+    SLANG_ASSERT(digest && digestSize >= 0);
+
+    static const char* hex = "0123456789abcdef";
+
+    String str;
+    const uint8_t* data = reinterpret_cast<const uint8_t*>(digest);
+    for (SlangInt i = 0; i < digestSize; ++i)
+    {
+        str.append(hex[data[i] >> 4]);
+        str.append(hex[data[i] & 0xf]);
+    }
+    return str;
+}
+
+/*static*/ bool DigestUtil::stringToDigest(const char* str, SlangInt strLength, void *digest, SlangInt digestSize)
+{
+    SLANG_ASSERT(str && strLength >= 0 && digest && digestSize >= 0);
+
+    if (strLength != digestSize * 2)
+    {
+        ::memset(digest, 0, digestSize);
+        return false;
+    }
+
+    uint8_t* data = reinterpret_cast<uint8_t*>(digest);
+    for (SlangInt i = 0; i < digestSize; ++i)
+    {
+        int upper = CharUtil::getHexDigitValue(str[i * 2]);
+        int lower = CharUtil::getHexDigitValue(str[i * 2 + 1]);
+        if (upper == -1 || lower == -1)
+        {
+            ::memset(digest, 0, digestSize);
+            return false;
+        }
+        data[i] = uint8_t(lower | upper << 4);;
+    }
+
+    return true;
+}
+
+// MD5
+
+MD5::MD5()
+{
+    init();
+}
+
+void MD5::init()
+{
+    m_lo = 0;
+    m_hi = 0;
+    m_a = 0x67452301;
+    m_b = 0xefcdab89;
+    m_c = 0x98badcfe;
+    m_d = 0x10325476;
+}
+
+void MD5::update(const void* data, SlangInt size)
+{
+    uint32_t saved_lo;
+    SlangInt used, available;
+
+    saved_lo = m_lo;
+    if ((m_lo = (saved_lo + size) & 0x1fffffff) < saved_lo)
+        m_hi++;
+    m_hi += (uint32_t)size >> 29;
+
+    used = saved_lo & 0x3f;
+
+    if (used) {
+        available = 64 - used;
+
+        if (size < available) {
+            ::memcpy(&m_buffer[used], data, size);
+            return;
+        }
+
+        ::memcpy(&m_buffer[used], data, available);
+        data = reinterpret_cast<const uint8_t*>(data) + available;
+        size -= available;
+        processBlock(m_buffer, 64);
+    }
+
+    if (size >= 64) {
+        data = processBlock(data, size & ~(SlangInt)0x3f);
+        size &= 0x3f;
+    }
+
+    ::memcpy(m_buffer, data, size);
+}
+
+MD5::Digest MD5::finalize()
+{
+    uint32_t used, available;
+
+    used = m_lo & 0x3f;
+
+    m_buffer[used++] = 0x80;
+
+    available = 64 - used;
+
+    if (available < 8) {
+        ::memset(&m_buffer[used], 0, available);
+        processBlock(m_buffer, 64);
+        used = 0;
+        available = 64;
+    }
+
+    ::memset(&m_buffer[used], 0, available - 8);
+
+    m_lo <<= 3;
+
+    m_buffer[56] = uint8_t(m_lo);
+    m_buffer[57] = uint8_t(m_lo >> 8);
+    m_buffer[58] = uint8_t(m_lo >> 16);
+    m_buffer[59] = uint8_t(m_lo >> 24);
+    m_buffer[60] = uint8_t(m_hi);
+    m_buffer[61] = uint8_t(m_hi >> 8);
+    m_buffer[62] = uint8_t(m_hi >> 16);
+    m_buffer[63] = uint8_t(m_hi >> 24);
+
+    processBlock(m_buffer, 64);
+
+    Digest digest;
+    digest.data[0] = m_a;
+    digest.data[1] = m_b;
+    digest.data[2] = m_c;
+    digest.data[3] = m_d;
+
+    return digest;
+}
+
+/*
+ * The basic MD5 functions.
+ *
+ * F and G are optimized compared to their RFC 1321 definitions for
+ * architectures that lack an AND-NOT instruction, just like in Colin Plumb's
+ * implementation.
+ */
+#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 H2(x, y, z)			((x) ^ ((y) ^ (z)))
+#define I(x, y, z)			((y) ^ ((x) | ~(z)))
+
+/*
+ * The MD5 transformation for all four rounds.
+ */
+#define STEP(f, a, b, c, d, x, t, s) \
+    (a) += f((b), (c), (d)) + (x) + (t); \
+    (a) = (((a) << (s)) | (((a) & 0xffffffff) >> (32 - (s)))); \
+    (a) += (b);
+
+/*
+ * SET reads 4 input bytes in little-endian byte order and stores them in a
+ * properly aligned word in host byte order.
+ */
+#define SET(n) \
+    (m_block[(n)] = \
+    (uint32_t)ptr[(n) * 4] | \
+    ((uint32_t)ptr[(n) * 4 + 1] << 8) | \
+    ((uint32_t)ptr[(n) * 4 + 2] << 16) | \
+    ((uint32_t)ptr[(n) * 4 + 3] << 24))
+#define GET(n) \
+    (m_block[(n)])
+
+const void* MD5::processBlock(const void* data, SlangInt size)
+{
+    const unsigned char* ptr;
+    ptr = (const unsigned char*)data;
+
+    uint32_t a = m_a;
+    uint32_t b = m_b;
+    uint32_t c = m_c;
+    uint32_t d = m_d;
+
+    do
+    {
+        uint32_t saved_a = a;
+        uint32_t saved_b = b;
+        uint32_t saved_c = c;
+        uint32_t saved_d = d;
+
+        /* Round 1 */
+        STEP(F, a, b, c, d, SET(0), 0xd76aa478, 7)
+        STEP(F, d, a, b, c, SET(1), 0xe8c7b756, 12)
+        STEP(F, c, d, a, b, SET(2), 0x242070db, 17)
+        STEP(F, b, c, d, a, SET(3), 0xc1bdceee, 22)
+        STEP(F, a, b, c, d, SET(4), 0xf57c0faf, 7)
+        STEP(F, d, a, b, c, SET(5), 0x4787c62a, 12)
+        STEP(F, c, d, a, b, SET(6), 0xa8304613, 17)
+        STEP(F, b, c, d, a, SET(7), 0xfd469501, 22)
+        STEP(F, a, b, c, d, SET(8), 0x698098d8, 7)
+        STEP(F, d, a, b, c, SET(9), 0x8b44f7af, 12)
+        STEP(F, c, d, a, b, SET(10), 0xffff5bb1, 17)
+        STEP(F, b, c, d, a, SET(11), 0x895cd7be, 22)
+        STEP(F, a, b, c, d, SET(12), 0x6b901122, 7)
+        STEP(F, d, a, b, c, SET(13), 0xfd987193, 12)
+        STEP(F, c, d, a, b, SET(14), 0xa679438e, 17)
+        STEP(F, b, c, d, a, SET(15), 0x49b40821, 22)
+
+        /* Round 2 */
+        STEP(G, a, b, c, d, GET(1), 0xf61e2562, 5)
+        STEP(G, d, a, b, c, GET(6), 0xc040b340, 9)
+        STEP(G, c, d, a, b, GET(11), 0x265e5a51, 14)
+        STEP(G, b, c, d, a, GET(0), 0xe9b6c7aa, 20)
+        STEP(G, a, b, c, d, GET(5), 0xd62f105d, 5)
+        STEP(G, d, a, b, c, GET(10), 0x02441453, 9)
+        STEP(G, c, d, a, b, GET(15), 0xd8a1e681, 14)
+        STEP(G, b, c, d, a, GET(4), 0xe7d3fbc8, 20)
+        STEP(G, a, b, c, d, GET(9), 0x21e1cde6, 5)
+        STEP(G, d, a, b, c, GET(14), 0xc33707d6, 9)
+        STEP(G, c, d, a, b, GET(3), 0xf4d50d87, 14)
+        STEP(G, b, c, d, a, GET(8), 0x455a14ed, 20)
+        STEP(G, a, b, c, d, GET(13), 0xa9e3e905, 5)
+        STEP(G, d, a, b, c, GET(2), 0xfcefa3f8, 9)
+        STEP(G, c, d, a, b, GET(7), 0x676f02d9, 14)
+        STEP(G, b, c, d, a, GET(12), 0x8d2a4c8a, 20)
+
+        /* Round 3 */
+        STEP(H, a, b, c, d, GET(5), 0xfffa3942, 4)
+        STEP(H2, d, a, b, c, GET(8), 0x8771f681, 11)
+        STEP(H, c, d, a, b, GET(11), 0x6d9d6122, 16)
+        STEP(H2, b, c, d, a, GET(14), 0xfde5380c, 23)
+        STEP(H, a, b, c, d, GET(1), 0xa4beea44, 4)
+        STEP(H2, d, a, b, c, GET(4), 0x4bdecfa9, 11)
+        STEP(H, c, d, a, b, GET(7), 0xf6bb4b60, 16)
+        STEP(H2, b, c, d, a, GET(10), 0xbebfbc70, 23)
+        STEP(H, a, b, c, d, GET(13), 0x289b7ec6, 4)
+        STEP(H2, d, a, b, c, GET(0), 0xeaa127fa, 11)
+        STEP(H, c, d, a, b, GET(3), 0xd4ef3085, 16)
+        STEP(H2, b, c, d, a, GET(6), 0x04881d05, 23)
+        STEP(H, a, b, c, d, GET(9), 0xd9d4d039, 4)
+        STEP(H2, d, a, b, c, GET(12), 0xe6db99e5, 11)
+        STEP(H, c, d, a, b, GET(15), 0x1fa27cf8, 16)
+        STEP(H2, b, c, d, a, GET(2), 0xc4ac5665, 23)
+
+        /* Round 4 */
+        STEP(I, a, b, c, d, GET(0), 0xf4292244, 6)
+        STEP(I, d, a, b, c, GET(7), 0x432aff97, 10)
+        STEP(I, c, d, a, b, GET(14), 0xab9423a7, 15)
+        STEP(I, b, c, d, a, GET(5), 0xfc93a039, 21)
+        STEP(I, a, b, c, d, GET(12), 0x655b59c3, 6)
+        STEP(I, d, a, b, c, GET(3), 0x8f0ccc92, 10)
+        STEP(I, c, d, a, b, GET(10), 0xffeff47d, 15)
+        STEP(I, b, c, d, a, GET(1), 0x85845dd1, 21)
+        STEP(I, a, b, c, d, GET(8), 0x6fa87e4f, 6)
+        STEP(I, d, a, b, c, GET(15), 0xfe2ce6e0, 10)
+        STEP(I, c, d, a, b, GET(6), 0xa3014314, 15)
+        STEP(I, b, c, d, a, GET(13), 0x4e0811a1, 21)
+        STEP(I, a, b, c, d, GET(4), 0xf7537e82, 6)
+        STEP(I, d, a, b, c, GET(11), 0xbd3af235, 10)
+        STEP(I, c, d, a, b, GET(2), 0x2ad7d2bb, 15)
+        STEP(I, b, c, d, a, GET(9), 0xeb86d391, 21)
+
+        a += saved_a;
+        b += saved_b;
+        c += saved_c;
+        d += saved_d;
+
+        ptr += 64;
+    }
+    while (size -= 64);
+
+    m_a = a;
+    m_b = b;
+    m_c = c;
+    m_d = d;
+
+    return ptr;
+}
+
+#undef F
+#undef G
+#undef H
+#undef H2
+#undef I
+#undef STEP
+#undef SET
+#undef GET
+
+/*static*/ MD5::Digest MD5::compute(const void* data, SlangInt size)
+{
+    MD5 md5;
+    md5.update(data, size);
+    return md5.finalize();
+}
+
+// SHA1
+
+SHA1::SHA1()
+{
+    init();
+}
+
+void SHA1::init()
+{
+    m_index = 0;
+    m_bits = 0;
+    m_state[0] = 0x67452301;
+    m_state[1] = 0xefcdab89;
+    m_state[2] = 0x98badcfe;
+    m_state[3] = 0x10325476;
+    m_state[4] = 0xc3d2e1f0;
+}
+
+void SHA1::update(const void* data, SlangInt len)
+{
+    if (!data || len <= 0)
+    {
+        return;
+    }
+
+    const uint8_t* ptr = reinterpret_cast<const uint8_t*>(data);
+
+    // Fill up buffer if not full.
+    while (len > 0 && m_index != 0)
+    {
+        addByte(*ptr++);
+        m_bits += 8;
+        len--;
+    }
+
+    // Process full blocks.
+    while (len >= sizeof(m_buf))
+    {
+        processBlock(ptr);
+        ptr += sizeof(m_buf);
+        len -= sizeof(m_buf);
+        m_bits += sizeof(m_buf) * 8;
+    }
+
+    // Process remaining bytes.
+    while (len > 0)
+    {
+        addByte(*ptr++);
+        m_bits += 8;
+        len--;
+    }
+}
+
+SHA1::Digest SHA1::finalize()
+{
+    // Finalize with 0x80, some zero padding and the length in bits.
+    addByte(0x80);
+    while (m_index % 64 != 56)
+    {
+        addByte(0);
+    }
+    for (int i = 7; i >= 0; --i)
+    {
+        addByte(uint8_t(m_bits >> i * 8));
+    }
+
+    Digest digest;
+    uint8_t* data = reinterpret_cast<uint8_t*>(digest.data);
+    for (int i = 0; i < 5; i++)
+    {
+        for (int j = 3; j >= 0; j--)
+        {
+            data[i * 4 + j] = (m_state[i] >> ((3 - j) * 8)) & 0xff;
+        }
+    }
+
+    return digest;
+}
+
+void SHA1::addByte(uint8_t byte)
+{
+    m_buf[m_index++] = byte;
+
+    if (m_index >= sizeof(m_buf))
+    {
+        m_index = 0;
+        processBlock(m_buf);
+    }
+}
+
+void SHA1::processBlock(const uint8_t* ptr)
+{
+    auto rol32 = [](uint32_t x, uint32_t n)
+    {
+        return (x << n) | (x >> (32 - n));
+    };
+
+    auto makeWord = [](const uint8_t* p)
+    {
+        return ((uint32_t)p[0] << 24) | ((uint32_t)p[1] << 16) | ((uint32_t)p[2] << 8) | (uint32_t)p[3];
+    };
+
+    const uint32_t c0 = 0x5a827999;
+    const uint32_t c1 = 0x6ed9eba1;
+    const uint32_t c2 = 0x8f1bbcdc;
+    const uint32_t c3 = 0xca62c1d6;
+
+    uint32_t a = m_state[0];
+    uint32_t b = m_state[1];
+    uint32_t c = m_state[2];
+    uint32_t d = m_state[3];
+    uint32_t e = m_state[4];
+
+    uint32_t w[16];
+
+    for (size_t i = 0; i < 16; i++)
+    {
+        w[i] = makeWord(ptr + i * 4);
+    }
+
+#define SHA1_LOAD(i) w[i&15] = rol32(w[(i + 13) & 15] ^ w[(i + 8) & 15] ^ w[(i + 2) & 15] ^ w[i & 15], 1);
+#define SHA1_ROUND_0(v,u,x,y,z,i)              z += ((u & (x ^ y)) ^ y) + w[i & 15] + c0 + rol32(v, 5); u = rol32(u, 30);
+#define SHA1_ROUND_1(v,u,x,y,z,i) SHA1_LOAD(i) z += ((u & (x ^ y)) ^ y) + w[i & 15] + c0 + rol32(v, 5); u = rol32(u, 30);
+#define SHA1_ROUND_2(v,u,x,y,z,i) SHA1_LOAD(i) z += (u ^ x ^ y) + w[i & 15] + c1 + rol32(v, 5); u = rol32(u, 30);
+#define SHA1_ROUND_3(v,u,x,y,z,i) SHA1_LOAD(i) z += (((u | x) & y) | (u & x)) + w[i & 15] + c2 + rol32(v, 5); u = rol32(u, 30);
+#define SHA1_ROUND_4(v,u,x,y,z,i) SHA1_LOAD(i) z += (u ^ x ^ y) + w[i & 15] + c3 + rol32(v, 5); u = rol32(u, 30);
+
+    SHA1_ROUND_0(a, b, c, d, e,  0);
+    SHA1_ROUND_0(e, a, b, c, d,  1);
+    SHA1_ROUND_0(d, e, a, b, c,  2);
+    SHA1_ROUND_0(c, d, e, a, b,  3);
+    SHA1_ROUND_0(b, c, d, e, a,  4);
+    SHA1_ROUND_0(a, b, c, d, e,  5);
+    SHA1_ROUND_0(e, a, b, c, d,  6);
+    SHA1_ROUND_0(d, e, a, b, c,  7);
+    SHA1_ROUND_0(c, d, e, a, b,  8);
+    SHA1_ROUND_0(b, c, d, e, a,  9);
+    SHA1_ROUND_0(a, b, c, d, e, 10);
+    SHA1_ROUND_0(e, a, b, c, d, 11);
+    SHA1_ROUND_0(d, e, a, b, c, 12);
+    SHA1_ROUND_0(c, d, e, a, b, 13);
+    SHA1_ROUND_0(b, c, d, e, a, 14);
+    SHA1_ROUND_0(a, b, c, d, e, 15);
+    SHA1_ROUND_1(e, a, b, c, d, 16);
+    SHA1_ROUND_1(d, e, a, b, c, 17);
+    SHA1_ROUND_1(c, d, e, a, b, 18);
+    SHA1_ROUND_1(b, c, d, e, a, 19);
+    SHA1_ROUND_2(a, b, c, d, e, 20);
+    SHA1_ROUND_2(e, a, b, c, d, 21);
+    SHA1_ROUND_2(d, e, a, b, c, 22);
+    SHA1_ROUND_2(c, d, e, a, b, 23);
+    SHA1_ROUND_2(b, c, d, e, a, 24);
+    SHA1_ROUND_2(a, b, c, d, e, 25);
+    SHA1_ROUND_2(e, a, b, c, d, 26);
+    SHA1_ROUND_2(d, e, a, b, c, 27);
+    SHA1_ROUND_2(c, d, e, a, b, 28);
+    SHA1_ROUND_2(b, c, d, e, a, 29);
+    SHA1_ROUND_2(a, b, c, d, e, 30);
+    SHA1_ROUND_2(e, a, b, c, d, 31);
+    SHA1_ROUND_2(d, e, a, b, c, 32);
+    SHA1_ROUND_2(c, d, e, a, b, 33);
+    SHA1_ROUND_2(b, c, d, e, a, 34);
+    SHA1_ROUND_2(a, b, c, d, e, 35);
+    SHA1_ROUND_2(e, a, b, c, d, 36);
+    SHA1_ROUND_2(d, e, a, b, c, 37);
+    SHA1_ROUND_2(c, d, e, a, b, 38);
+    SHA1_ROUND_2(b, c, d, e, a, 39);
+    SHA1_ROUND_3(a, b, c, d, e, 40);
+    SHA1_ROUND_3(e, a, b, c, d, 41);
+    SHA1_ROUND_3(d, e, a, b, c, 42);
+    SHA1_ROUND_3(c, d, e, a, b, 43);
+    SHA1_ROUND_3(b, c, d, e, a, 44);
+    SHA1_ROUND_3(a, b, c, d, e, 45);
+    SHA1_ROUND_3(e, a, b, c, d, 46);
+    SHA1_ROUND_3(d, e, a, b, c, 47);
+    SHA1_ROUND_3(c, d, e, a, b, 48);
+    SHA1_ROUND_3(b, c, d, e, a, 49);
+    SHA1_ROUND_3(a, b, c, d, e, 50);
+    SHA1_ROUND_3(e, a, b, c, d, 51);
+    SHA1_ROUND_3(d, e, a, b, c, 52);
+    SHA1_ROUND_3(c, d, e, a, b, 53);
+    SHA1_ROUND_3(b, c, d, e, a, 54);
+    SHA1_ROUND_3(a, b, c, d, e, 55);
+    SHA1_ROUND_3(e, a, b, c, d, 56);
+    SHA1_ROUND_3(d, e, a, b, c, 57);
+    SHA1_ROUND_3(c, d, e, a, b, 58);
+    SHA1_ROUND_3(b, c, d, e, a, 59);
+    SHA1_ROUND_4(a, b, c, d, e, 60);
+    SHA1_ROUND_4(e, a, b, c, d, 61);
+    SHA1_ROUND_4(d, e, a, b, c, 62);
+    SHA1_ROUND_4(c, d, e, a, b, 63);
+    SHA1_ROUND_4(b, c, d, e, a, 64);
+    SHA1_ROUND_4(a, b, c, d, e, 65);
+    SHA1_ROUND_4(e, a, b, c, d, 66);
+    SHA1_ROUND_4(d, e, a, b, c, 67);
+    SHA1_ROUND_4(c, d, e, a, b, 68);
+    SHA1_ROUND_4(b, c, d, e, a, 69);
+    SHA1_ROUND_4(a, b, c, d, e, 70);
+    SHA1_ROUND_4(e, a, b, c, d, 71);
+    SHA1_ROUND_4(d, e, a, b, c, 72);
+    SHA1_ROUND_4(c, d, e, a, b, 73);
+    SHA1_ROUND_4(b, c, d, e, a, 74);
+    SHA1_ROUND_4(a, b, c, d, e, 75);
+    SHA1_ROUND_4(e, a, b, c, d, 76);
+    SHA1_ROUND_4(d, e, a, b, c, 77);
+    SHA1_ROUND_4(c, d, e, a, b, 78);
+    SHA1_ROUND_4(b, c, d, e, a, 79);
+
+#undef SHA1_LOAD
+#undef SHA1_ROUND_0
+#undef SHA1_ROUND_1
+#undef SHA1_ROUND_2
+#undef SHA1_ROUND_3
+#undef SHA1_ROUND_4
+
+    m_state[0] += a;
+    m_state[1] += b;
+    m_state[2] += c;
+    m_state[3] += d;
+    m_state[4] += e;
+}
+
+/* static */SHA1::Digest SHA1::compute(const void* data, SlangInt size)
+{
+    SHA1 sha1;
+    sha1.update(data, size);
+    return sha1.finalize();
+}
+
+}
+
+
+/*
+ * This is an OpenSSL-compatible implementation of the RSA Data Security, Inc.
+ * MD5 Message-Digest Algorithm (RFC 1321).
+ *
+ * Homepage:
+ * http://openwall.info/wiki/people/solar/software/public-domain-source-code/md5
+ *
+ * Author:
+ * Alexander Peslyak, better known as Solar Designer <solar at openwall.com>
+ *
+ * This software was written by Alexander Peslyak in 2001.  No copyright is
+ * claimed, and the software is hereby placed in the public domain.
+ * In case this attempt to disclaim copyright and place the software in the
+ * public domain is deemed null and void, then the software is
+ * Copyright (c) 2001 Alexander Peslyak and it is hereby released to the
+ * general public under the following terms:
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted.
+ *
+ * There's ABSOLUTELY NO WARRANTY, express or implied.
+ *
+ * (This is a heavily cut-down "BSD license".)
+ *
+ * This differs from Colin Plumb's older public domain implementation in that
+ * no exactly 32-bit integer data type is required (any 32-bit or wider
+ * unsigned integer data type will do), there's no compile-time endianness
+ * configuration, and the function prototypes match OpenSSL's.  No code from
+ * Colin Plumb's implementation has been reused; this comment merely compares
+ * the properties of the two independent implementations.
+ *
+ * The primary goals of this implementation are portability and ease of use.
+ * It is meant to be fast, but not as fast as possible.  Some known
+ * optimizations are not included to reduce source code size and avoid
+ * compile-time configuration.
+ */
+
+/*
+ * This is free and unencumbered software released into the public domain.
+ * 
+ * Anyone is free to copy, modify, publish, use, compile, sell, or
+ * distribute this software, either in source code form or as a compiled
+ * binary, for any purpose, commercial or non-commercial, and by any
+ * means.
+ * 
+ * In jurisdictions that recognize copyright laws, the author or authors
+ * of this software dedicate any and all copyright interest in the
+ * software to the public domain. We make this dedication for the benefit
+ * of the public at large and to the detriment of our heirs and
+ * successors. We intend this dedication to be an overt act of
+ * relinquishment in perpetuity of all present and future rights to this
+ * software under copyright law.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ * 
+ * For more information, please refer to <http://unlicense.org>
+ */