target/alpha: Use float64_to_int64_modulo for CVTTQ

For the most part we can use the new generic routine,
though exceptions need some post-processing to sort
invalid from integer overflow.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230527141910.1885950-4-richard.henderson@linaro.org>

target/alpha/fpu_helper.c

@@ -453,78 +453,29 @@ uint64_t helper_cvtqs(CPUAlphaState *env, uint64_t a)
 
 static uint64_t do_cvttq(CPUAlphaState *env, uint64_t a, int roundmode)
 {
-    uint64_t frac, ret = 0;
-    uint32_t exp, sign, exc = 0;
-    int shift;
+    float64 fa;
+    int64_t ret;
+    uint32_t exc;
 
-    sign = (a >> 63);
-    exp = (uint32_t)(a >> 52) & 0x7ff;
-    frac = a & 0xfffffffffffffull;
+    fa = t_to_float64(a);
+    ret = float64_to_int64_modulo(fa, roundmode, &FP_STATUS);
 
-    if (exp == 0) {
-        if (unlikely(frac != 0) && !env->fp_status.flush_inputs_to_zero) {
-            goto do_underflow;
-        }
-    } else if (exp == 0x7ff) {
-        exc = FPCR_INV;
-    } else {
-        /* Restore implicit bit.  */
-        frac |= 0x10000000000000ull;
-
-        shift = exp - 1023 - 52;
-        if (shift >= 0) {
-            /* In this case the number is so large that we must shift
-               the fraction left.  There is no rounding to do.  */
-            if (shift < 64) {
-                ret = frac << shift;
-            }
-            /* Check for overflow.  Note the special case of -0x1p63.  */
-            if (shift >= 11 && a != 0xC3E0000000000000ull) {
-                exc = FPCR_IOV | FPCR_INE;
-            }
-        } else {
-            uint64_t round;
-
-            /* In this case the number is smaller than the fraction as
-               represented by the 52 bit number.  Here we must think
-               about rounding the result.  Handle this by shifting the
-               fractional part of the number into the high bits of ROUND.
-               This will let us efficiently handle round-to-nearest.  */
-            shift = -shift;
-            if (shift < 63) {
-                ret = frac >> shift;
-                round = frac << (64 - shift);
-            } else {
-                /* The exponent is so small we shift out everything.
-                   Leave a sticky bit for proper rounding below.  */
-            do_underflow:
-                round = 1;
-            }
+    exc = get_float_exception_flags(&FP_STATUS);
+    if (unlikely(exc)) {
+        set_float_exception_flags(0, &FP_STATUS);
 
-            if (round) {
-                exc = FPCR_INE;
-                switch (roundmode) {
-                case float_round_nearest_even:
-                    if (round == (1ull << 63)) {
-                        /* Fraction is exactly 0.5; round to even.  */
-                        ret += (ret & 1);
-                    } else if (round > (1ull << 63)) {
-                        ret += 1;
-                    }
-                    break;
-                case float_round_to_zero:
-                    break;
-                case float_round_up:
-                    ret += 1 - sign;
-                    break;
-                case float_round_down:
-                    ret += sign;
-                    break;
-                }
+        /* We need to massage the resulting exceptions. */
+        if (exc & float_flag_invalid_cvti) {
+            /* Overflow, either normal or infinity. */
+            if (float64_is_infinity(fa)) {
+                exc = FPCR_INV;
+            } else {
+                exc = FPCR_IOV | FPCR_INE;
             }
-        }
-        if (sign) {
-            ret = -ret;
+        } else if (exc & float_flag_invalid) {
+            exc = FPCR_INV;
+        } else if (exc & float_flag_inexact) {
+            exc = FPCR_INE;
         }
     }
     env->error_code = exc;