Add support for 128-bit arithmetic

The memory API supports 64-bit buses (e.g. PCI).  A size on such a bus cannot
be represented with a 64-bit data type, if both 0 and the entire address
space size are to be represented.  Futhermore, any address arithemetic may
overflow and return unexpected results.

Introduce a 128-bit signed integer type for use in such cases.  Addition,
subtraction, and comparison are the only operations supported.

Signed-off-by: Avi Kivity <avi@redhat.com>

int128.h

@@ -0,0 +1,116 @@
+#ifndef INT128_H
+#define INT128_H
+
+typedef struct Int128 Int128;
+
+struct Int128 {
+    uint64_t lo;
+    int64_t hi;
+};
+
+static inline Int128 int128_make64(uint64_t a)
+{
+    return (Int128) { a, 0 };
+}
+
+static inline uint64_t int128_get64(Int128 a)
+{
+    assert(!a.hi);
+    return a.lo;
+}
+
+static inline Int128 int128_zero(void)
+{
+    return int128_make64(0);
+}
+
+static inline Int128 int128_one(void)
+{
+    return int128_make64(1);
+}
+
+static inline Int128 int128_2_64(void)
+{
+    return (Int128) { 0, 1 };
+}
+
+static inline Int128 int128_add(Int128 a, Int128 b)
+{
+    Int128 r = { a.lo + b.lo, a.hi + b.hi };
+    r.hi += (r.lo < a.lo) || (r.lo < b.lo);
+    return r;
+}
+
+static inline Int128 int128_neg(Int128 a)
+{
+    a.lo = ~a.lo;
+    a.hi = ~a.hi;
+    return int128_add(a, int128_one());
+}
+
+static inline Int128 int128_sub(Int128 a, Int128 b)
+{
+    return int128_add(a, int128_neg(b));
+}
+
+static inline bool int128_nonneg(Int128 a)
+{
+    return a.hi >= 0;
+}
+
+static inline bool int128_eq(Int128 a, Int128 b)
+{
+    return a.lo == b.lo && a.hi == b.hi;
+}
+
+static inline bool int128_ne(Int128 a, Int128 b)
+{
+    return !int128_eq(a, b);
+}
+
+static inline bool int128_ge(Int128 a, Int128 b)
+{
+    return int128_nonneg(int128_sub(a, b));
+}
+
+static inline bool int128_lt(Int128 a, Int128 b)
+{
+    return !int128_ge(a, b);
+}
+
+static inline bool int128_le(Int128 a, Int128 b)
+{
+    return int128_ge(b, a);
+}
+
+static inline bool int128_gt(Int128 a, Int128 b)
+{
+    return !int128_le(a, b);
+}
+
+static inline bool int128_nz(Int128 a)
+{
+    return a.lo || a.hi;
+}
+
+static inline Int128 int128_min(Int128 a, Int128 b)
+{
+    return int128_le(a, b) ? a : b;
+}
+
+static inline Int128 int128_max(Int128 a, Int128 b)
+{
+    return int128_ge(a, b) ? a : b;
+}
+
+static inline void int128_addto(Int128 *a, Int128 b)
+{
+    *a = int128_add(*a, b);
+}
+
+static inline void int128_subfrom(Int128 *a, Int128 b)
+{
+    *a = int128_sub(*a, b);
+}
+
+#endif