Make engine dep-free/standalone and add Wasm target

libc-lite.h

@@ -0,0 +1,80 @@
+
+#include <limits.h>
+#include <stddef.h>
+#include <stdint.h>
+
+static uint64_t g_rand_seed = 1;
+
+void my_srand(uint64_t n)
+{
+    g_rand_seed = n == 0 ? 1 : n;
+}
+
+uint64_t my_rand64()
+{
+    /* 
+     * Xorshift RNG [1] + multiply
+     * [1]: https://www.jstatsoft.org/article/view/v008i14/916 */
+    uint64_t x = g_rand_seed;
+    x ^= x >> 12ULL;
+    x ^= x << 25ULL;
+    x ^= x >> 27ULL;
+    g_rand_seed = x;
+    return x * 2685821657736338717ULL;
+}
+
+static int my_tolower(int ch)
+{
+    return ch >= 'A' && ch <= 'Z'
+        ? ch - 'A' + 'a'
+        : ch;
+}
+
+static int my_isdigit(int ch)
+{
+    return ch >= '0' && ch <= '9';
+}
+
+void* my_memset(void *b, int c, size_t len)
+{
+    unsigned char* x = b;
+    unsigned char ch = (unsigned char)c;
+    for (size_t i = 0; i < len; ++i) {
+        x[i] = ch;
+    }
+    return b;
+}
+
+void* my_memcpy(void* restrict dst, void const* restrict src, size_t n)
+{
+    uint8_t* d = dst;
+    uint8_t const* s = src;
+
+    for (size_t i = 0; i < n; ++i) {
+        d[i] = s[i];
+    }
+
+    return dst;
+}
+
+int my_memcmp(void const* s1, void const* s2, size_t n)
+{
+    /* todo: SIMD optimize or use 64 bit strides initially if optimizer
+       doesn't catch this */
+    int8_t const* a = s1;
+    int8_t const* b = s2;
+    for (size_t i = 0; i < n; ++i) {
+        int8_t diff = a[i] - b[i];
+        if (diff)
+            return diff;
+    }
+    return 0;
+}
+
+size_t strlen(char const* s)
+{
+    size_t n = 0;
+    while (s[n++])
+        ;
+    return n;
+}