host-utils: move checks out of divu128/divs128

In preparation for changing the divu128/divs128 implementations
to allow for quotients larger than 64 bits, move the div-by-zero
and overflow checks to the callers.

Signed-off-by: Luis Pires <luis.pires@eldorado.org.br>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20211025191154.350831-2-luis.pires@eldorado.org.br>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

2 files changed, 16 insertions, 25 deletions

diff --git a/include/hw/clock.h b/include/hw/clock.h
index 11f67fb..7443e6c 100644
--- a/include/hw/clock.h
+++ b/include/hw/clock.h
@@ -324,8 +324,9 @@ static inline uint64_t clock_ns_to_ticks(const Clock *clk, uint64_t ns)
         return 0;
     }
     /*
-     * Ignore divu128() return value as we've caught div-by-zero and don't
-     * need different behaviour for overflow.
+     * BUG: when CONFIG_INT128 is not defined, the current implementation of
+     * divu128 does not return a valid truncated quotient, so the result will
+     * be wrong.
      */
     divu128(&lo, &hi, clk->period);
     return lo;
diff --git a/include/qemu/host-utils.h b/include/qemu/host-utils.h
index ca9f3f0..e82e623 100644
--- a/include/qemu/host-utils.h
+++ b/include/qemu/host-utils.h
@@ -52,36 +52,26 @@ static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c)
     return (__int128_t)a * b / c;
 }
 
-static inline int divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor)
-{
-    if (divisor == 0) {
-        return 1;
-    } else {
-        __uint128_t dividend = ((__uint128_t)*phigh << 64) | *plow;
-        __uint128_t result = dividend / divisor;
-        *plow = result;
-        *phigh = dividend % divisor;
-        return result > UINT64_MAX;
-    }
+static inline void divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor)
+{
+    __uint128_t dividend = ((__uint128_t)*phigh << 64) | *plow;
+    __uint128_t result = dividend / divisor;
+    *plow = result;
+    *phigh = dividend % divisor;
 }
 
-static inline int divs128(int64_t *plow, int64_t *phigh, int64_t divisor)
+static inline void divs128(int64_t *plow, int64_t *phigh, int64_t divisor)
 {
-    if (divisor == 0) {
-        return 1;
-    } else {
-        __int128_t dividend = ((__int128_t)*phigh << 64) | (uint64_t)*plow;
-        __int128_t result = dividend / divisor;
-        *plow = result;
-        *phigh = dividend % divisor;
-        return result != *plow;
-    }
+    __int128_t dividend = ((__int128_t)*phigh << 64) | (uint64_t)*plow;
+    __int128_t result = dividend / divisor;
+    *plow = result;
+    *phigh = dividend % divisor;
 }
 #else
 void muls64(uint64_t *plow, uint64_t *phigh, int64_t a, int64_t b);
 void mulu64(uint64_t *plow, uint64_t *phigh, uint64_t a, uint64_t b);
-int divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor);
-int divs128(int64_t *plow, int64_t *phigh, int64_t divisor);
+void divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor);
+void divs128(int64_t *plow, int64_t *phigh, int64_t divisor);
 
 static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c)
 {