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Implement left shift

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This commit is contained in:
Victor Zverovich 2019-09-07 17:38:27 -07:00
parent ac71d853be
commit 0887887e23
2 changed files with 31 additions and 4 deletions
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25
include/fmt/format-inl.h
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@ -398,13 +398,14 @@ class fp {
// Normalizes the value converted from double and multiplied by (1 << SHIFT).
template <int SHIFT> friend fp normalize(fp value) {
// Handle subnormals.
const auto shifted_implicit_bit = implicit_bit << SHIFT;
const auto shifted_implicit_bit = fp::implicit_bit << SHIFT;
while ((value.f & shifted_implicit_bit) == 0) {
value.f <<= 1;
--value.e;
}
// Subtract 1 to account for hidden bit.
const auto offset = significand_size - double_significand_size - SHIFT - 1;
const auto offset =
fp::significand_size - fp::double_significand_size - SHIFT - 1;
value.f <<= offset;
value.e -= offset;
return value;
@ -490,6 +491,18 @@ class bigint {
bigint(const bigint&) = delete;
void operator=(const bigint&) = delete;
bigint& operator<<=(int shift) {
assert(shift >= 0 && shift < bigit_bits);
bigit carry = 0;
for (size_t i = 0, n = bigits_.size(); i < n; ++i) {
bigit c = shift != 0 ? bigits_[i] >> (bigit_bits - shift) : 0;
bigits_[i] = (bigits_[i] << shift) + carry;
carry = c;
}
if (carry != 0) bigits_.push_back(carry);
return *this;
}
};
enum round_direction { unknown, up, down };
@ -712,6 +725,10 @@ template <int GRISU_VERSION> struct grisu_shortest_handler {
}
};
FMT_API void fallback_format(const fp& value) {
(void)value; // TODO
}
template <typename Double,
enable_if_t<(sizeof(Double) == sizeof(uint64_t)), int>>
FMT_API bool grisu_format(Double value, buffer<char>& buf, int precision,
@ -765,13 +782,13 @@ FMT_API bool grisu_format(Double value, buffer<char>& buf, int precision,
result = grisu_gen_digits(upper, upper.f - lower.f, exp, handler);
size = handler.size;
if (result == digits::error) {
// TODO: use fallback
fallback_format(fp_value);
return false;
}
} else {
++lower.f; // \tilde{M}^- + 1 ulp -> M^-_{\uparrow}.
--upper.f; // \tilde{M}^+ - 1 ulp -> M^+_{\downarrow}.
grisu_shortest_handler<2> handler{buf.data(), 0, (upper - fp_value).f};
grisu_shortest_handler<2> handler{buf.data(), 0, (upper - normalized).f};
result = grisu_gen_digits(upper, upper.f - lower.f, exp, handler);
size = handler.size;
assert(result != digits::error);

10
test/format-impl-test.cc
View File

@ -33,6 +33,16 @@ TEST(BigIntTest, Construct) {
EXPECT_EQ("123456789abcedf0", fmt::format("{}", bigint(0x123456789abcedf0)));
}
TEST(BigIntTest, ShiftLeft) {
bigint n(0x42);
n <<= 0;
EXPECT_EQ("42", fmt::format("{}", n));
n <<= 1;
EXPECT_EQ("84", fmt::format("{}", n));
n <<= 25;
EXPECT_EQ("108000000", fmt::format("{}", n));
}
template <bool is_iec559> void test_construct_from_double() {
fmt::print("warning: double is not IEC559, skipping FP tests\n");
}