host-utils: Introduce mulu128

Signed-off-by: Luis Pires <luis.pires@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20211029192417.400707-6-luis.pires@eldorado.org.br>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

include/qemu/host-utils.h

@@ -590,6 +590,42 @@ static inline bool umul64_overflow(uint64_t x, uint64_t y, uint64_t *ret)
 #endif
 }
 
+/*
+ * Unsigned 128x64 multiplication.
+ * Returns true if the result got truncated to 128 bits.
+ * Otherwise, returns false and the multiplication result via plow and phigh.
+ */
+static inline bool mulu128(uint64_t *plow, uint64_t *phigh, uint64_t factor)
+{
+#if defined(CONFIG_INT128) && \
+    (__has_builtin(__builtin_mul_overflow) || __GNUC__ >= 5)
+    bool res;
+    __uint128_t r;
+    __uint128_t f = ((__uint128_t)*phigh << 64) | *plow;
+    res = __builtin_mul_overflow(f, factor, &r);
+
+    *plow = r;
+    *phigh = r >> 64;
+
+    return res;
+#else
+    uint64_t dhi = *phigh;
+    uint64_t dlo = *plow;
+    uint64_t ahi;
+    uint64_t blo, bhi;
+
+    if (dhi == 0) {
+        mulu64(plow, phigh, dlo, factor);
+        return false;
+    }
+
+    mulu64(plow, &ahi, dlo, factor);
+    mulu64(&blo, &bhi, dhi, factor);
+
+    return uadd64_overflow(ahi, blo, phigh) || bhi != 0;
+#endif
+}
+
 /**
  * uadd64_carry - addition with carry-in and carry-out
  * @x, @y: addends