optimize dec2float

Author: 9il

source/mir/bignum/internal/dec2float.d

@@ -140,40 +140,76 @@ T decimalToFloatImpl(T)(ulong coefficient, long exponent)
     if (_expect(-ExponentM <= exponent && exponent <= ExponentM, true))
     {
         auto c = coefficient.Fp!64;
+
         T approx = void;
-        version (all)
-        {{
-            auto z = c.extendedMul!true(_load!wordBits(exponent));
-            approx = z.opCast!(T, true);
-            long bitsDiff = (cast(ulong) z.opCast!(Fp!wordBits).coefficient & mask) - half;
-            uint slop = 3 * (exponent < 0);
-            if (_expect(approx > T.min_normal && (bitsDiff < 0 ? -bitsDiff : bitsDiff) > slop, true))
-                return approx;
-        }}
-        static if (T.mant_dig < 64)
-        {{
-            auto z = c.extendedMul!true(_load!128(exponent));
-            approx = z.opCast!(T, true);
-            auto bitsDiff = (z.opCast!(Fp!128).coefficient & bigMask) - bigHalf;
-            if (bitsDiff.signBit)
-                bitsDiff = UInt!128.init - bitsDiff;
-            uint slop = 3 * (exponent < 0);
-            if (_expect(approx > T.min_normal && bitsDiff > slop, true))
-                return approx;
-        }}
-
-        if (0 <= exponent)
-        {
-            if (exponent <= 55) // exact exponent
-                return approx;
-        }
-        else
+
+        if (exponent < 0)
         {
+            version (all)
+            {{
+                auto z = c.extendedMul!true(_load!wordBits(exponent));
+                approx = z.opCast!(T, true);
+                long bitsDiff = (cast(ulong) z.opCast!(Fp!wordBits).coefficient & mask) - half;
+                uint slop = 3;
+                if (_expect(approx > T.min_normal && (bitsDiff < 0 ? -bitsDiff : bitsDiff) > slop, true))
+                    return approx;
+            }}
+
             if (-exponent <= MaxFpPow5!T)
             {
                 auto e = _load!wordBits(-exponent);
                 return coefficient / e.opCast!(T, true);
             }
+
+            static if (T.mant_dig < 64)
+            {{
+                auto z = c.extendedMul!true(_load!128(exponent));
+                approx = z.opCast!(T, true);
+                auto bitsDiff = (z.opCast!(Fp!128).coefficient & bigMask) - bigHalf;
+                if (bitsDiff.signBit)
+                    bitsDiff = UInt!128.init - bitsDiff;
+                uint slop = 3;
+                if (_expect(approx > T.min_normal && bitsDiff > slop, true))
+                    return approx;
+            }}
+
+        }
+        else
+        {
+            version (all)
+            {{
+                auto z = c.extendedMul!true(_load!wordBits(exponent));
+                approx = z.opCast!(T, true);
+
+                if (exponent <= 27) // exact exponent
+                {
+                    return approx;
+                }
+
+                long bitsDiff = (cast(ulong) z.opCast!(Fp!wordBits).coefficient & mask) - half;
+                uint slop;
+                if (_expect(approx > T.min_normal && (bitsDiff < 0 ? -bitsDiff : bitsDiff) > slop, true))
+                    return approx;
+            }}
+
+            static if (T.mant_dig < 64)
+            {{
+                auto z = c.extendedMul!true(_load!128(exponent));
+                approx = z.opCast!(T, true);
+
+                if (exponent <= 55) // exact exponent
+                {
+                    return approx;
+                }
+
+                auto bitsDiff = (z.opCast!(Fp!128).coefficient & bigMask) - bigHalf;
+                if (bitsDiff.signBit)
+                    bitsDiff = UInt!128.init - bitsDiff;
+                uint slop;
+                if (_expect(approx > T.min_normal && bitsDiff > slop, true))
+                    return approx;
+            }}
+
         }
     }
     size_t[ulong.sizeof / size_t.sizeof] coefficients;