Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

kernel/core/string.c

@@ -0,0 +1,113 @@
+#include "types.h"
+#include "x86.h"
+
+void*
+memset(void *dst, int c, uint64 n)
+{
+  uint64 c64;
+
+  if ((addr_t)dst % 8 == 0 && n % 8 == 0) {
+    c &= 0xFF;
+    c64 = (uint64)c;
+    c64 = (c64 << 56) | (c64 << 48) | (c64 << 40) | (c64 << 32) |
+          (c64 << 24) | (c64 << 16) | (c64 << 8) | c64;
+    stosq(dst, c64, n / 8);
+  } else {
+    stosb(dst, c, n);
+  }
+  return dst;
+}
+
+int
+memcmp(const void *v1, const void *v2, uint n)
+{
+  const uchar *s1, *s2;
+
+  s1 = v1;
+  s2 = v2;
+  while(n-- > 0){
+    if(*s1 != *s2)
+      return *s1 - *s2;
+    s1++, s2++;
+  }
+
+  return 0;
+}
+
+void*
+memmove(void *dst, const void *src, uint n)
+{
+  const char *s;
+  char *d;
+
+  s = src;
+  d = dst;
+  if(s < d && s + n > d){
+    s += n;
+    d += n;
+    while(n-- > 0)
+      *--d = *--s;
+  } else
+    while(n-- > 0)
+      *d++ = *s++;
+
+  return dst;
+}
+
+void*
+memcpy(void *dst, const void *src, uint n)
+{
+  return memmove(dst, src, n);
+}
+
+int
+strncmp(const char *p, const char *q, uint n)
+{
+  while(n > 0 && *p && *p == *q)
+    n--, p++, q++;
+  if(n == 0)
+    return 0;
+  return (uchar)*p - (uchar)*q;
+}
+
+char*
+strncpy(char *s, const char *t, int n)
+{
+  char *os = s;
+  while(n-- > 0 && (*s++ = *t++) != 0)
+    ;
+  while(n-- > 0)
+    *s++ = 0;
+  return os;
+}
+
+char*
+safestrcpy(char *s, const char *t, int n)
+{
+  char *os = s;
+  if(n <= 0)
+    return os;
+  while(--n > 0 && (*s++ = *t++) != 0)
+    ;
+  *s = 0;
+  return os;
+}
+
+int
+strlen(const char *s)
+{
+  int n;
+
+  for(n = 0; s[n]; n++)
+    ;
+  return n;
+}
+
+int
+strnlen(const char *s, int max)
+{
+  int n;
+  for(n = 0; n < max && s[n]; n++)
+    ;
+  return n;
+}