Fix #157 (#158)

multipleOfPowerOf2 only works for exponents < 64.

In this case here we have 0 < m10 < 2^64, so m10 can never
be a multiple of 2^p if p >= 64.

ryu/d2s_intrinsics.h

@@ -215,6 +215,7 @@ static inline bool multipleOfPowerOf5(const uint64_t value, const uint32_t p) {
 // Returns true if value is divisible by 2^p.
 static inline bool multipleOfPowerOf2(const uint64_t value, const uint32_t p) {
   assert(value != 0);
+  assert(p < 64);
   // __builtin_ctzll doesn't appear to be faster here.
   return (value & ((1ull << p) - 1)) == 0;
 }

ryu/s2d.c

@@ -184,7 +184,7 @@ enum Status s2d_n(const char * buffer, const int len, double * result) {
     // This can only be the case if 2^e2 divides m10 * 10^e10, which in turn requires that the
     // largest power of 2 that divides m10 + e10 is greater than e2. If e2 is less than e10, then
     // the result must be exact. Otherwise we use the existing multipleOfPowerOf2 function.
-    trailingZeros = e2 < e10 || multipleOfPowerOf2(m10, e2 - e10);
+    trailingZeros = e2 < e10 || (e2 - e10 < 64 && multipleOfPowerOf2(m10, e2 - e10));
   } else {
     e2 = floor_log2(m10) + e10 - ceil_log2pow5(-e10) - (DOUBLE_MANTISSA_BITS + 1);
     int j = e2 - e10 + ceil_log2pow5(-e10) - 1 + DOUBLE_POW5_INV_BITCOUNT;

ryu/tests/s2d_test.cc

@@ -85,3 +85,7 @@ TEST(S2dTest, Overflow) {
 TEST(S2dTest, TableSizeDenormal) {
   EXPECT_S2D(5e-324, "4.9406564584124654e-324");
 }
+
+TEST(S2dTest, Issue157) {
+  EXPECT_S2D(1.2999999999999999E+154, "1.2999999999999999E+154");
+}