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Implement Grisu boundary computation

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This commit is contained in:
Victor Zverovich 2018-08-25 11:39:38 -07:00
parent a11eb3a090
commit 569ac91e0b
3 changed files with 85 additions and 51 deletions
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14
include/fmt/format.h
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@ -297,6 +297,7 @@ class fp {
static FMT_CONSTEXPR_DECL const int significand_size =
sizeof(significand_type) * char_size;
fp(): f(0), e(0) {}
fp(uint64_t f, int e): f(f), e(e) {}
// Constructs fp from an IEEE754 double. It is a template to prevent compile
@ -335,6 +336,19 @@ class fp {
f <<= offset;
e -= offset;
}
// Compute lower and upper boundaries (m^- and m^+ in the Grisu paper), where
// a boundary is a value half way between the number and its predecessor
// (lower) or successor (upper). The upper boundary is normalized and lower
// has the same exponent but may be not normalized.
void compute_boundaries(fp &lower, fp &upper) const {
lower = f == implicit_bit ?
fp((f << 2) - 1, e - 2) : fp((f << 1) - 1, e - 1);
upper = fp((f << 1) + 1, e - 1);
upper.normalize<1>(); // 1 is to account for the exponent shift above.
lower.f <<= lower.e - upper.e;
lower.e = upper.e;
}
};
// Returns an fp number representing x - y. Result may not be normalized.

51
test/core-test.cc
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@ -36,7 +36,6 @@ using fmt::basic_format_arg;
using fmt::internal::basic_buffer;
using fmt::basic_memory_buffer;
using fmt::string_view;
using fmt::internal::fp;
using fmt::internal::value;
using testing::_;
@ -879,56 +878,6 @@ TEST(UtilTest, ParseNonnegativeInt) {
fmt::format_error, "number is too big");
}
template <bool is_iec559>
void test_construct_from_double() {
fmt::print("warning: double is not IEC559, skipping FP tests\n");
}
template <>
void test_construct_from_double<true>() {
auto v = fp(1.23);
EXPECT_EQ(v.f, 0x13ae147ae147aeu);
EXPECT_EQ(v.e, -52);
}
TEST(FPTest, ConstructFromDouble) {
test_construct_from_double<std::numeric_limits<double>::is_iec559>();
}
TEST(FPTest, Normalize) {
auto v = fp(0xbeef, 42);
v.normalize();
EXPECT_EQ(0xbeef000000000000, v.f);
EXPECT_EQ(-6, v.e);
}
TEST(FPTest, Subtract) {
auto v = fp(123, 1) - fp(102, 1);
EXPECT_EQ(v.f, 21u);
EXPECT_EQ(v.e, 1);
}
TEST(FPTest, Multiply) {
auto v = fp(123ULL << 32, 4) * fp(56ULL << 32, 7);
EXPECT_EQ(v.f, 123u * 56u);
EXPECT_EQ(v.e, 4 + 7 + 64);
v = fp(123ULL << 32, 4) * fp(567ULL << 31, 8);
EXPECT_EQ(v.f, (123 * 567 + 1u) / 2);
EXPECT_EQ(v.e, 4 + 8 + 64);
}
TEST(FPTest, GetCachedPower) {
typedef std::numeric_limits<double> limits;
for (auto exp = limits::min_exponent; exp <= limits::max_exponent; ++exp) {
int dec_exp = 0;
auto fp = fmt::internal::get_cached_power(exp, dec_exp);
EXPECT_LE(exp, fp.e);
int dec_exp_step = 8;
EXPECT_LE(fp.e, exp + dec_exp_step * log2(10));
EXPECT_DOUBLE_EQ(pow(10, dec_exp), ldexp(fp.f, fp.e));
}
}
TEST(IteratorTest, CountingIterator) {
fmt::internal::counting_iterator<char> it;
auto prev = it++;

71
test/format-test.cc
View File

@ -31,6 +31,77 @@ using fmt::format_error;
using fmt::string_view;
using fmt::memory_buffer;
using fmt::wmemory_buffer;
using fmt::internal::fp;
template <bool is_iec559>
void test_construct_from_double() {
fmt::print("warning: double is not IEC559, skipping FP tests\n");
}
template <>
void test_construct_from_double<true>() {
auto v = fp(1.23);
EXPECT_EQ(v.f, 0x13ae147ae147aeu);
EXPECT_EQ(v.e, -52);
}
TEST(FPTest, ConstructFromDouble) {
test_construct_from_double<std::numeric_limits<double>::is_iec559>();
}
TEST(FPTest, Normalize) {
auto v = fp(0xbeef, 42);
v.normalize();
EXPECT_EQ(0xbeef000000000000, v.f);
EXPECT_EQ(-6, v.e);
}
TEST(FPTest, ComputeBoundariesSubnormal) {
auto v = fp(0xbeef, 42);
fp lower, upper;
v.compute_boundaries(lower, upper);
EXPECT_EQ(0xbeee800000000000, lower.f);
EXPECT_EQ(-6, lower.e);
EXPECT_EQ(0xbeef800000000000, upper.f);
EXPECT_EQ(-6, upper.e);
}
TEST(FPTest, ComputeBoundaries) {
auto v = fp(0x10000000000000, 42);
fp lower, upper;
v.compute_boundaries(lower, upper);
EXPECT_EQ(0x7ffffffffffffe00, lower.f);
EXPECT_EQ(31, lower.e);
EXPECT_EQ(0x8000000000000400, upper.f);
EXPECT_EQ(31, upper.e);
}
TEST(FPTest, Subtract) {
auto v = fp(123, 1) - fp(102, 1);
EXPECT_EQ(v.f, 21u);
EXPECT_EQ(v.e, 1);
}
TEST(FPTest, Multiply) {
auto v = fp(123ULL << 32, 4) * fp(56ULL << 32, 7);
EXPECT_EQ(v.f, 123u * 56u);
EXPECT_EQ(v.e, 4 + 7 + 64);
v = fp(123ULL << 32, 4) * fp(567ULL << 31, 8);
EXPECT_EQ(v.f, (123 * 567 + 1u) / 2);
EXPECT_EQ(v.e, 4 + 8 + 64);
}
TEST(FPTest, GetCachedPower) {
typedef std::numeric_limits<double> limits;
for (auto exp = limits::min_exponent; exp <= limits::max_exponent; ++exp) {
int dec_exp = 0;
auto fp = fmt::internal::get_cached_power(exp, dec_exp);
EXPECT_LE(exp, fp.e);
int dec_exp_step = 8;
EXPECT_LE(fp.e, exp + dec_exp_step * log2(10));
EXPECT_DOUBLE_EQ(pow(10, dec_exp), ldexp(fp.f, fp.e));
}
}
namespace {