host-utils: Implemented signed 256-by-128 division

Based on already existing QEMU implementation created a signed
256 bit by 128 bit division needed to implement the vector divide
extended signed quadword instruction from PowerISA 3.1

Signed-off-by: Lucas Mateus Castro (alqotel) <lucas.araujo@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220525134954.85056-6-lucas.araujo@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

include/qemu/host-utils.h

@@ -851,4 +851,5 @@ static inline uint64_t udiv_qrnnd(uint64_t *r, uint64_t n1,
 }
 
 Int128 divu256(Int128 *plow, Int128 *phigh, Int128 divisor);
+Int128 divs256(Int128 *plow, Int128 *phigh, Int128 divisor);
 #endif

util/host-utils.c

@@ -395,3 +395,54 @@ Int128 divu256(Int128 *plow, Int128 *phigh, Int128 divisor)
         return rem;
     }
 }
+
+/*
+ * Signed 256-by-128 division.
+ * Returns quotient via plow and phigh.
+ * Also returns the remainder via the function return value.
+ */
+Int128 divs256(Int128 *plow, Int128 *phigh, Int128 divisor)
+{
+    bool neg_quotient = false, neg_remainder = false;
+    Int128 unsig_hi = *phigh, unsig_lo = *plow;
+    Int128 rem;
+
+    if (!int128_nonneg(*phigh)) {
+        neg_quotient = !neg_quotient;
+        neg_remainder = !neg_remainder;
+
+        if (!int128_nz(unsig_lo)) {
+            unsig_hi = int128_neg(unsig_hi);
+        } else {
+            unsig_hi = int128_not(unsig_hi);
+            unsig_lo = int128_neg(unsig_lo);
+        }
+    }
+
+    if (!int128_nonneg(divisor)) {
+        neg_quotient = !neg_quotient;
+
+        divisor = int128_neg(divisor);
+    }
+
+    rem = divu256(&unsig_lo, &unsig_hi, divisor);
+
+    if (neg_quotient) {
+        if (!int128_nz(unsig_lo)) {
+            *phigh = int128_neg(unsig_hi);
+            *plow = int128_zero();
+        } else {
+            *phigh = int128_not(unsig_hi);
+            *plow = int128_neg(unsig_lo);
+        }
+    } else {
+        *phigh = unsig_hi;
+        *plow = unsig_lo;
+    }
+
+    if (neg_remainder) {
+        return int128_neg(rem);
+    } else {
+        return rem;
+    }
+}