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-rw-r--r--absl/strings/BUILD.bazel1
-rw-r--r--absl/strings/CMakeLists.txt1
-rw-r--r--absl/strings/cord.cc2
-rw-r--r--absl/strings/internal/str_format/convert_test.cc230
-rw-r--r--absl/strings/internal/str_format/float_conversion.cc281
-rw-r--r--absl/strings/str_cat.cc8
6 files changed, 499 insertions, 24 deletions
diff --git a/absl/strings/BUILD.bazel b/absl/strings/BUILD.bazel
index 8220896d..ef412639 100644
--- a/absl/strings/BUILD.bazel
+++ b/absl/strings/BUILD.bazel
@@ -720,6 +720,7 @@ cc_test(
visibility = ["//visibility:private"],
deps = [
":str_format_internal",
+ ":strings",
"//absl/base:raw_logging_internal",
"//absl/types:optional",
"@com_google_googletest//:gtest_main",
diff --git a/absl/strings/CMakeLists.txt b/absl/strings/CMakeLists.txt
index c0ea0c8e..d7237231 100644
--- a/absl/strings/CMakeLists.txt
+++ b/absl/strings/CMakeLists.txt
@@ -475,6 +475,7 @@ absl_cc_test(
COPTS
${ABSL_TEST_COPTS}
DEPS
+ absl::strings
absl::str_format_internal
absl::raw_logging_internal
absl::int128
diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc
index 68f53987..8ecffc4b 100644
--- a/absl/strings/cord.cc
+++ b/absl/strings/cord.cc
@@ -495,7 +495,7 @@ static CordRep* NewSubstring(CordRep* child, size_t offset, size_t length) {
// This will trigger LNK2005 in MSVC.
#ifndef COMPILER_MSVC
-const unsigned char Cord::InlineRep::kMaxInline;
+constexpr unsigned char Cord::InlineRep::kMaxInline;
#endif // COMPILER_MSVC
inline void Cord::InlineRep::set_data(const char* data, size_t n,
diff --git a/absl/strings/internal/str_format/convert_test.cc b/absl/strings/internal/str_format/convert_test.cc
index e37d0546..488d4cd4 100644
--- a/absl/strings/internal/str_format/convert_test.cc
+++ b/absl/strings/internal/str_format/convert_test.cc
@@ -12,6 +12,7 @@
#include "gtest/gtest.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/strings/internal/str_format/bind.h"
+#include "absl/strings/match.h"
#include "absl/types/optional.h"
namespace absl {
@@ -19,6 +20,13 @@ ABSL_NAMESPACE_BEGIN
namespace str_format_internal {
namespace {
+struct NativePrintfTraits {
+ bool hex_float_has_glibc_rounding;
+ bool hex_float_prefers_denormal_repr;
+ bool hex_float_uses_minimal_precision_when_not_specified;
+ bool hex_float_optimizes_leading_digit_bit_count;
+};
+
template <typename T, size_t N>
size_t ArraySize(T (&)[N]) {
return N;
@@ -118,6 +126,63 @@ std::string StrPrint(const char *format, ...) {
return result;
}
+NativePrintfTraits VerifyNativeImplementationImpl() {
+ NativePrintfTraits result;
+
+ // >>> hex_float_has_glibc_rounding. To have glibc's rounding behavior we need
+ // to meet three requirements:
+ //
+ // - The threshold for rounding up is 8 (for e.g. MSVC uses 9).
+ // - If the digits lower than than the 8 are non-zero then we round up.
+ // - If the digits lower than the 8 are all zero then we round toward even.
+ //
+ // The numbers below represent all the cases covering {below,at,above} the
+ // threshold (8) with both {zero,non-zero} lower bits and both {even,odd}
+ // preceding digits.
+ const double d0079 = 65657.0; // 0x1.0079p+16
+ const double d0179 = 65913.0; // 0x1.0179p+16
+ const double d0080 = 65664.0; // 0x1.0080p+16
+ const double d0180 = 65920.0; // 0x1.0180p+16
+ const double d0081 = 65665.0; // 0x1.0081p+16
+ const double d0181 = 65921.0; // 0x1.0181p+16
+ result.hex_float_has_glibc_rounding =
+ StartsWith(StrPrint("%.2a", d0079), "0x1.00") &&
+ StartsWith(StrPrint("%.2a", d0179), "0x1.01") &&
+ StartsWith(StrPrint("%.2a", d0080), "0x1.00") &&
+ StartsWith(StrPrint("%.2a", d0180), "0x1.02") &&
+ StartsWith(StrPrint("%.2a", d0081), "0x1.01") &&
+ StartsWith(StrPrint("%.2a", d0181), "0x1.02");
+
+ // >>> hex_float_prefers_denormal_repr. Formatting `denormal` on glibc yields
+ // "0x0.0000000000001p-1022", whereas on std libs that don't use denormal
+ // representation it would either be 0x1p-1074 or 0x1.0000000000000-1074.
+ const double denormal = std::numeric_limits<double>::denorm_min();
+ result.hex_float_prefers_denormal_repr =
+ StartsWith(StrPrint("%a", denormal), "0x0.0000000000001");
+
+ // >>> hex_float_uses_minimal_precision_when_not_specified. Some (non-glibc)
+ // libs will format the following as "0x1.0079000000000p+16".
+ result.hex_float_uses_minimal_precision_when_not_specified =
+ (StrPrint("%a", d0079) == "0x1.0079p+16");
+
+ // >>> hex_float_optimizes_leading_digit_bit_count. The number 1.5, when
+ // formatted by glibc should yield "0x1.8p+0" for `double` and "0xcp-3" for
+ // `long double`, i.e., number of bits in the leading digit is adapted to the
+ // number of bits in the mantissa.
+ const double d_15 = 1.5;
+ const long double ld_15 = 1.5;
+ result.hex_float_optimizes_leading_digit_bit_count =
+ StartsWith(StrPrint("%a", d_15), "0x1.8") &&
+ StartsWith(StrPrint("%La", ld_15), "0xc");
+
+ return result;
+}
+
+const NativePrintfTraits &VerifyNativeImplementation() {
+ static NativePrintfTraits native_traits = VerifyNativeImplementationImpl();
+ return native_traits;
+}
+
class FormatConvertTest : public ::testing::Test { };
template <typename T>
@@ -476,6 +541,7 @@ TEST_F(FormatConvertTest, Uint128) {
template <typename Floating>
void TestWithMultipleFormatsHelper(const std::vector<Floating> &floats) {
+ const NativePrintfTraits &native_traits = VerifyNativeImplementation();
// Reserve the space to ensure we don't allocate memory in the output itself.
std::string str_format_result;
str_format_result.reserve(1 << 20);
@@ -493,13 +559,23 @@ void TestWithMultipleFormatsHelper(const std::vector<Floating> &floats) {
'e', 'E'}) {
std::string fmt_str = std::string(fmt) + f;
- if (fmt == absl::string_view("%.5000") && f != 'f' && f != 'F') {
+ if (fmt == absl::string_view("%.5000") && f != 'f' && f != 'F' &&
+ f != 'a' && f != 'A') {
// This particular test takes way too long with snprintf.
// Disable for the case we are not implementing natively.
continue;
}
+ if ((f == 'a' || f == 'A') &&
+ !native_traits.hex_float_has_glibc_rounding) {
+ continue;
+ }
+
for (Floating d : floats) {
+ if (!native_traits.hex_float_prefers_denormal_repr &&
+ (f == 'a' || f == 'A') && std::fpclassify(d) == FP_SUBNORMAL) {
+ continue;
+ }
int i = -10;
FormatArgImpl args[2] = {FormatArgImpl(d), FormatArgImpl(i)};
UntypedFormatSpecImpl format(fmt_str);
@@ -766,6 +842,111 @@ TEST_F(FormatConvertTest, DoubleRound) {
"1837869002408041296803276054561138153076171875");
}
+TEST_F(FormatConvertTest, DoubleRoundA) {
+ const NativePrintfTraits &native_traits = VerifyNativeImplementation();
+ std::string s;
+ const auto format = [&](const char *fmt, double d) -> std::string & {
+ s.clear();
+ FormatArgImpl args[1] = {FormatArgImpl(d)};
+ AppendPack(&s, UntypedFormatSpecImpl(fmt), absl::MakeSpan(args));
+ if (native_traits.hex_float_has_glibc_rounding) {
+ EXPECT_EQ(StrPrint(fmt, d), s);
+ }
+ return s;
+ };
+
+ // 0x1.00018000p+100
+ const double on_boundary_odd = 1267679614447900152596896153600.0;
+ EXPECT_EQ(format("%.0a", on_boundary_odd), "0x1p+100");
+ EXPECT_EQ(format("%.1a", on_boundary_odd), "0x1.0p+100");
+ EXPECT_EQ(format("%.2a", on_boundary_odd), "0x1.00p+100");
+ EXPECT_EQ(format("%.3a", on_boundary_odd), "0x1.000p+100");
+ EXPECT_EQ(format("%.4a", on_boundary_odd), "0x1.0002p+100"); // round
+ EXPECT_EQ(format("%.5a", on_boundary_odd), "0x1.00018p+100");
+ EXPECT_EQ(format("%.6a", on_boundary_odd), "0x1.000180p+100");
+
+ // 0x1.00028000p-2
+ const double on_boundary_even = 0.250009536743164062500;
+ EXPECT_EQ(format("%.0a", on_boundary_even), "0x1p-2");
+ EXPECT_EQ(format("%.1a", on_boundary_even), "0x1.0p-2");
+ EXPECT_EQ(format("%.2a", on_boundary_even), "0x1.00p-2");
+ EXPECT_EQ(format("%.3a", on_boundary_even), "0x1.000p-2");
+ EXPECT_EQ(format("%.4a", on_boundary_even), "0x1.0002p-2"); // no round
+ EXPECT_EQ(format("%.5a", on_boundary_even), "0x1.00028p-2");
+ EXPECT_EQ(format("%.6a", on_boundary_even), "0x1.000280p-2");
+
+ // 0x1.00018001p+1
+ const double slightly_over = 2.00004577683284878730773925781250;
+ EXPECT_EQ(format("%.0a", slightly_over), "0x1p+1");
+ EXPECT_EQ(format("%.1a", slightly_over), "0x1.0p+1");
+ EXPECT_EQ(format("%.2a", slightly_over), "0x1.00p+1");
+ EXPECT_EQ(format("%.3a", slightly_over), "0x1.000p+1");
+ EXPECT_EQ(format("%.4a", slightly_over), "0x1.0002p+1");
+ EXPECT_EQ(format("%.5a", slightly_over), "0x1.00018p+1");
+ EXPECT_EQ(format("%.6a", slightly_over), "0x1.000180p+1");
+
+ // 0x1.00017fffp+0
+ const double slightly_under = 1.000022887950763106346130371093750;
+ EXPECT_EQ(format("%.0a", slightly_under), "0x1p+0");
+ EXPECT_EQ(format("%.1a", slightly_under), "0x1.0p+0");
+ EXPECT_EQ(format("%.2a", slightly_under), "0x1.00p+0");
+ EXPECT_EQ(format("%.3a", slightly_under), "0x1.000p+0");
+ EXPECT_EQ(format("%.4a", slightly_under), "0x1.0001p+0");
+ EXPECT_EQ(format("%.5a", slightly_under), "0x1.00018p+0");
+ EXPECT_EQ(format("%.6a", slightly_under), "0x1.000180p+0");
+ EXPECT_EQ(format("%.7a", slightly_under), "0x1.0001800p+0");
+
+ // 0x1.1b3829ac28058p+3
+ const double hex_value = 8.85060580848964661981881363317370414733886718750;
+ EXPECT_EQ(format("%.0a", hex_value), "0x1p+3");
+ EXPECT_EQ(format("%.1a", hex_value), "0x1.2p+3");
+ EXPECT_EQ(format("%.2a", hex_value), "0x1.1bp+3");
+ EXPECT_EQ(format("%.3a", hex_value), "0x1.1b4p+3");
+ EXPECT_EQ(format("%.4a", hex_value), "0x1.1b38p+3");
+ EXPECT_EQ(format("%.5a", hex_value), "0x1.1b383p+3");
+ EXPECT_EQ(format("%.6a", hex_value), "0x1.1b382ap+3");
+ EXPECT_EQ(format("%.7a", hex_value), "0x1.1b3829bp+3");
+ EXPECT_EQ(format("%.8a", hex_value), "0x1.1b3829acp+3");
+ EXPECT_EQ(format("%.9a", hex_value), "0x1.1b3829ac3p+3");
+ EXPECT_EQ(format("%.10a", hex_value), "0x1.1b3829ac28p+3");
+ EXPECT_EQ(format("%.11a", hex_value), "0x1.1b3829ac280p+3");
+ EXPECT_EQ(format("%.12a", hex_value), "0x1.1b3829ac2806p+3");
+ EXPECT_EQ(format("%.13a", hex_value), "0x1.1b3829ac28058p+3");
+ EXPECT_EQ(format("%.14a", hex_value), "0x1.1b3829ac280580p+3");
+ EXPECT_EQ(format("%.15a", hex_value), "0x1.1b3829ac2805800p+3");
+ EXPECT_EQ(format("%.16a", hex_value), "0x1.1b3829ac28058000p+3");
+ EXPECT_EQ(format("%.17a", hex_value), "0x1.1b3829ac280580000p+3");
+ EXPECT_EQ(format("%.18a", hex_value), "0x1.1b3829ac2805800000p+3");
+ EXPECT_EQ(format("%.19a", hex_value), "0x1.1b3829ac28058000000p+3");
+ EXPECT_EQ(format("%.20a", hex_value), "0x1.1b3829ac280580000000p+3");
+ EXPECT_EQ(format("%.21a", hex_value), "0x1.1b3829ac2805800000000p+3");
+
+ // 0x1.0818283848586p+3
+ const double hex_value2 = 8.2529488658208371987257123691961169242858886718750;
+ EXPECT_EQ(format("%.0a", hex_value2), "0x1p+3");
+ EXPECT_EQ(format("%.1a", hex_value2), "0x1.1p+3");
+ EXPECT_EQ(format("%.2a", hex_value2), "0x1.08p+3");
+ EXPECT_EQ(format("%.3a", hex_value2), "0x1.082p+3");
+ EXPECT_EQ(format("%.4a", hex_value2), "0x1.0818p+3");
+ EXPECT_EQ(format("%.5a", hex_value2), "0x1.08183p+3");
+ EXPECT_EQ(format("%.6a", hex_value2), "0x1.081828p+3");
+ EXPECT_EQ(format("%.7a", hex_value2), "0x1.0818284p+3");
+ EXPECT_EQ(format("%.8a", hex_value2), "0x1.08182838p+3");
+ EXPECT_EQ(format("%.9a", hex_value2), "0x1.081828385p+3");
+ EXPECT_EQ(format("%.10a", hex_value2), "0x1.0818283848p+3");
+ EXPECT_EQ(format("%.11a", hex_value2), "0x1.08182838486p+3");
+ EXPECT_EQ(format("%.12a", hex_value2), "0x1.081828384858p+3");
+ EXPECT_EQ(format("%.13a", hex_value2), "0x1.0818283848586p+3");
+ EXPECT_EQ(format("%.14a", hex_value2), "0x1.08182838485860p+3");
+ EXPECT_EQ(format("%.15a", hex_value2), "0x1.081828384858600p+3");
+ EXPECT_EQ(format("%.16a", hex_value2), "0x1.0818283848586000p+3");
+ EXPECT_EQ(format("%.17a", hex_value2), "0x1.08182838485860000p+3");
+ EXPECT_EQ(format("%.18a", hex_value2), "0x1.081828384858600000p+3");
+ EXPECT_EQ(format("%.19a", hex_value2), "0x1.0818283848586000000p+3");
+ EXPECT_EQ(format("%.20a", hex_value2), "0x1.08182838485860000000p+3");
+ EXPECT_EQ(format("%.21a", hex_value2), "0x1.081828384858600000000p+3");
+}
+
// We don't actually store the results. This is just to exercise the rest of the
// machinery.
struct NullSink {
@@ -797,6 +978,7 @@ TEST_F(FormatConvertTest, LongDouble) {
// implementation against the native one there.
return;
#endif // _MSC_VER
+ const NativePrintfTraits &native_traits = VerifyNativeImplementation();
const char *const kFormats[] = {"%", "%.3", "%8.5", "%9", "%.5000",
"%.60", "%+", "% ", "%-10"};
@@ -839,12 +1021,20 @@ TEST_F(FormatConvertTest, LongDouble) {
'e', 'E'}) {
std::string fmt_str = std::string(fmt) + 'L' + f;
- if (fmt == absl::string_view("%.5000") && f != 'f' && f != 'F') {
+ if (fmt == absl::string_view("%.5000") && f != 'f' && f != 'F' &&
+ f != 'a' && f != 'A') {
// This particular test takes way too long with snprintf.
// Disable for the case we are not implementing natively.
continue;
}
+ if (f == 'a' || f == 'A') {
+ if (!native_traits.hex_float_has_glibc_rounding ||
+ !native_traits.hex_float_optimizes_leading_digit_bit_count) {
+ continue;
+ }
+ }
+
for (auto d : doubles) {
FormatArgImpl arg(d);
UntypedFormatSpecImpl format(fmt_str);
@@ -860,6 +1050,7 @@ TEST_F(FormatConvertTest, LongDouble) {
}
TEST_F(FormatConvertTest, IntAsDouble) {
+ const NativePrintfTraits &native_traits = VerifyNativeImplementation();
const int kMin = std::numeric_limits<int>::min();
const int kMax = std::numeric_limits<int>::max();
const int ia[] = {
@@ -875,14 +1066,16 @@ TEST_F(FormatConvertTest, IntAsDouble) {
const char *fmt;
};
const double dx = static_cast<double>(fx);
- const Expectation kExpect[] = {
- { __LINE__, StrPrint("%f", dx), "%f" },
- { __LINE__, StrPrint("%12f", dx), "%12f" },
- { __LINE__, StrPrint("%.12f", dx), "%.12f" },
- { __LINE__, StrPrint("%12a", dx), "%12a" },
- { __LINE__, StrPrint("%.12a", dx), "%.12a" },
+ std::vector<Expectation> expect = {
+ {__LINE__, StrPrint("%f", dx), "%f"},
+ {__LINE__, StrPrint("%12f", dx), "%12f"},
+ {__LINE__, StrPrint("%.12f", dx), "%.12f"},
+ {__LINE__, StrPrint("%.12a", dx), "%.12a"},
};
- for (const Expectation &e : kExpect) {
+ if (native_traits.hex_float_uses_minimal_precision_when_not_specified) {
+ expect.push_back({__LINE__, StrPrint("%12a", dx), "%12a"});
+ }
+ for (const Expectation &e : expect) {
SCOPED_TRACE(e.line);
SCOPED_TRACE(e.fmt);
UntypedFormatSpecImpl format(e.fmt);
@@ -927,6 +1120,25 @@ TEST_F(FormatConvertTest, ExpectedFailures) {
EXPECT_TRUE(FormatFails("%*d", ""));
}
+// Sanity check to make sure that we are testing what we think we're testing on
+// e.g. the x86_64+glibc platform.
+TEST_F(FormatConvertTest, GlibcHasCorrectTraits) {
+#if !defined(__GLIBC__) || !defined(__x86_64__)
+ return;
+#endif
+ const NativePrintfTraits &native_traits = VerifyNativeImplementation();
+ // If one of the following tests break then it is either because the above PP
+ // macro guards failed to exclude a new platform (likely) or because something
+ // has changed in the implemention of glibc sprintf float formatting behavior.
+ // If the latter, then the code that computes these flags needs to be
+ // revisited and/or possibly the StrFormat implementation.
+ EXPECT_TRUE(native_traits.hex_float_has_glibc_rounding);
+ EXPECT_TRUE(native_traits.hex_float_prefers_denormal_repr);
+ EXPECT_TRUE(
+ native_traits.hex_float_uses_minimal_precision_when_not_specified);
+ EXPECT_TRUE(native_traits.hex_float_optimizes_leading_digit_bit_count);
+}
+
} // namespace
} // namespace str_format_internal
ABSL_NAMESPACE_END
diff --git a/absl/strings/internal/str_format/float_conversion.cc b/absl/strings/internal/str_format/float_conversion.cc
index 39fc5f60..6eb7b9fc 100644
--- a/absl/strings/internal/str_format/float_conversion.cc
+++ b/absl/strings/internal/str_format/float_conversion.cc
@@ -15,6 +15,7 @@
#include "absl/functional/function_ref.h"
#include "absl/meta/type_traits.h"
#include "absl/numeric/int128.h"
+#include "absl/strings/numbers.h"
#include "absl/types/optional.h"
#include "absl/types/span.h"
@@ -453,26 +454,31 @@ Padding ExtraWidthToPadding(size_t total_size, const FormatState &state) {
}
}
-void FinalPrint(absl::string_view data, int trailing_zeros,
- const FormatState &state) {
+void FinalPrint(const FormatState &state, absl::string_view data,
+ int padding_offset, int trailing_zeros,
+ absl::string_view data_postfix) {
if (state.conv.width() < 0) {
// No width specified. Fast-path.
if (state.sign_char != '\0') state.sink->Append(1, state.sign_char);
state.sink->Append(data);
state.sink->Append(trailing_zeros, '0');
+ state.sink->Append(data_postfix);
return;
}
- auto padding =
- ExtraWidthToPadding((state.sign_char != '\0' ? 1 : 0) + data.size() +
- static_cast<size_t>(trailing_zeros),
- state);
+ auto padding = ExtraWidthToPadding((state.sign_char != '\0' ? 1 : 0) +
+ data.size() + data_postfix.size() +
+ static_cast<size_t>(trailing_zeros),
+ state);
state.sink->Append(padding.left_spaces, ' ');
if (state.sign_char != '\0') state.sink->Append(1, state.sign_char);
+ // Padding in general needs to be inserted somewhere in the middle of `data`.
+ state.sink->Append(data.substr(0, padding_offset));
state.sink->Append(padding.zeros, '0');
- state.sink->Append(data);
+ state.sink->Append(data.substr(padding_offset));
state.sink->Append(trailing_zeros, '0');
+ state.sink->Append(data_postfix);
state.sink->Append(padding.right_spaces, ' ');
}
@@ -525,10 +531,11 @@ void FormatFFast(Int v, int exp, const FormatState &state) {
// In `alt` mode (flag #) we keep the `.` even if there are no fractional
// digits. In non-alt mode, we strip it.
if (!state.ShouldPrintDot()) --size;
- FinalPrint(absl::string_view(integral_digits_start, size),
+ FinalPrint(state, absl::string_view(integral_digits_start, size),
+ /*padding_offset=*/0,
static_cast<int>(state.precision - (fractional_digits_end -
fractional_digits_start)),
- state);
+ /*data_postfix=*/"");
}
// Slow %f formatter for when the shifted value does not fit in a uint128, and
@@ -655,6 +662,257 @@ void FormatF(Int mantissa, int exp, const FormatState &state) {
return FormatFFast(mantissa, exp, state);
}
+// Grab the group of four bits (nibble) from `n`. E.g., nibble 1 corresponds to
+// bits 4-7.
+template <typename Int>
+uint8_t GetNibble(Int n, int nibble_index) {
+ constexpr Int mask_low_nibble = Int{0xf};
+ int shift = nibble_index * 4;
+ n &= mask_low_nibble << shift;
+ return static_cast<uint8_t>((n >> shift) & 0xf);
+}
+
+// Add one to the given nibble, applying carry to higher nibbles. Returns true
+// if overflow, false otherwise.
+template <typename Int>
+bool IncrementNibble(int nibble_index, Int *n) {
+ constexpr int kShift = sizeof(Int) * 8 - 1;
+ constexpr int kNumNibbles = sizeof(Int) * 8 / 4;
+ Int before = *n >> kShift;
+ // Here we essentially want to take the number 1 and move it into the requsted
+ // nibble, then add it to *n to effectively increment the nibble. However,
+ // ASan will complain if we try to shift the 1 beyond the limits of the Int,
+ // i.e., if the nibble_index is out of range. So therefore we check for this
+ // and if we are out of range we just add 0 which leaves *n unchanged, which
+ // seems like the reasonable thing to do in that case.
+ *n +=
+ ((nibble_index * 4 >= sizeof(Int) * 8) ? 0
+ : (Int{1} << (nibble_index * 4)));
+ Int after = *n >> kShift;
+ return (before && !after) || (nibble_index >= kNumNibbles);
+}
+
+// Return a mask with 1's in the given nibble and all lower nibbles.
+template <typename Int>
+Int MaskUpToNibbleInclusive(int nibble_index) {
+ constexpr int kNumNibbles = sizeof(Int) * 8 / 4;
+ static const Int ones = ~Int{0};
+ return ones >> std::max(0, 4 * (kNumNibbles - nibble_index - 1));
+}
+
+// Return a mask with 1's below the given nibble.
+template <typename Int>
+Int MaskUpToNibbleExclusive(int nibble_index) {
+ return nibble_index <= 0 ? 0 : MaskUpToNibbleInclusive<Int>(nibble_index - 1);
+}
+
+template <typename Int>
+Int MoveToNibble(uint8_t nibble, int nibble_index) {
+ return Int{nibble} << (4 * nibble_index);
+}
+
+// Given mantissa size, find optimal # of mantissa bits to put in initial digit.
+//
+// In the hex representation we keep a single hex digit to the left of the dot.
+// However, the question as to how many bits of the mantissa should be put into
+// that hex digit in theory is arbitrary, but in practice it is optimal to
+// choose based on the size of the mantissa. E.g., for a `double`, there are 53
+// mantissa bits, so that means that we should put 1 bit to the left of the dot,
+// thereby leaving 52 bits to the right, which is evenly divisible by four and
+// thus all fractional digits represent actual precision. For a `long double`,
+// on the other hand, there are 64 bits of mantissa, thus we can use all four
+// bits for the initial hex digit and still have a number left over (60) that is
+// a multiple of four. Once again, the goal is to have all fractional digits
+// represent real precision.
+template <typename Float>
+constexpr int HexFloatLeadingDigitSizeInBits() {
+ return std::numeric_limits<Float>::digits % 4 > 0
+ ? std::numeric_limits<Float>::digits % 4
+ : 4;
+}
+
+// This function captures the rounding behavior of glibc for hex float
+// representations. E.g. when rounding 0x1.ab800000 to a precision of .2
+// ("%.2a") glibc will round up because it rounds toward the even number (since
+// 0xb is an odd number, it will round up to 0xc). However, when rounding at a
+// point that is not followed by 800000..., it disregards the parity and rounds
+// up if > 8 and rounds down if < 8.
+template <typename Int>
+bool HexFloatNeedsRoundUp(Int mantissa, int final_nibble_displayed) {
+ // If the last nibble (hex digit) to be displayed is the lowest on in the
+ // mantissa then that means that we don't have any further nibbles to inform
+ // rounding, so don't round.
+ if (final_nibble_displayed <= 0) {
+ return false;
+ }
+ int rounding_nibble_idx = final_nibble_displayed - 1;
+ constexpr int kTotalNibbles = sizeof(Int) * 8 / 4;
+ assert(final_nibble_displayed <= kTotalNibbles);
+ Int mantissa_up_to_rounding_nibble_inclusive =
+ mantissa & MaskUpToNibbleInclusive<Int>(rounding_nibble_idx);
+ Int eight = MoveToNibble<Int>(8, rounding_nibble_idx);
+ if (mantissa_up_to_rounding_nibble_inclusive != eight) {
+ return mantissa_up_to_rounding_nibble_inclusive > eight;
+ }
+ // Nibble in question == 8.
+ uint8_t should_round_at_8 =
+ (final_nibble_displayed >= kTotalNibbles)
+ ? true
+ : (GetNibble(mantissa, final_nibble_displayed) % 2 == 1);
+ return should_round_at_8;
+}
+
+// Stores values associated with a Float type needed by the FormatA
+// implementation in order to avoid templatizing that function by the Float
+// type.
+struct HexFloatTypeParams {
+ template <typename Float>
+ explicit HexFloatTypeParams(Float)
+ : min_exponent(std::numeric_limits<Float>::min_exponent - 1),
+ leading_digit_size_bits(HexFloatLeadingDigitSizeInBits<Float>()) {
+ assert(leading_digit_size_bits >= 1 && leading_digit_size_bits <= 4);
+ }
+
+ int min_exponent;
+ int leading_digit_size_bits;
+};
+
+// Hex Float Rounding. First check if we need to round; if so, then we do that
+// by manipulating (incrementing) the mantissa, that way we can later print the
+// mantissa digits by iterating through them in the same way regardless of
+// whether a rounding happened.
+template <typename Int>
+void FormatARound(bool precision_specified, const FormatState &state,
+ uint8_t *leading, Int *mantissa, int *exp) {
+ constexpr int kTotalNibbles = sizeof(Int) * 8 / 4;
+ // Index of the last nibble that we could display given precision.
+ int final_nibble_displayed =
+ precision_specified ? std::max(0, (kTotalNibbles - state.precision)) : 0;
+ if (HexFloatNeedsRoundUp(*mantissa, final_nibble_displayed)) {
+ // Need to round up.
+ bool overflow = IncrementNibble(final_nibble_displayed, mantissa);
+ *leading += (overflow ? 1 : 0);
+ if (ABSL_PREDICT_FALSE(*leading > 15)) {
+ // We have overflowed the leading digit. This would mean that we would
+ // need two hex digits to the left of the dot, which is not allowed. So
+ // adjust the mantissa and exponent so that the result is always 1.0eXXX.
+ *leading = 1;
+ *mantissa = 0;
+ *exp += 4;
+ }
+ }
+ // Now that we have handled a possible round-up we can go ahead and zero out
+ // all the nibbles of the mantissa that we won't need.
+ if (precision_specified) {
+ *mantissa &= ~MaskUpToNibbleExclusive<Int>(final_nibble_displayed);
+ }
+}
+
+template <typename Int>
+void FormatANormalize(const HexFloatTypeParams float_traits, uint8_t *leading,
+ Int *mantissa, int *exp) {
+ constexpr int kIntBits = sizeof(Int) * 8;
+ static const Int kHighIntBit = Int{1} << (kIntBits - 1);
+ const int kLeadDigitBitsCount = float_traits.leading_digit_size_bits;
+ // Normalize mantissa so that highest bit set is in MSB position, unless we
+ // get interrupted by the exponent threshold.
+ while (*mantissa && !(*mantissa & kHighIntBit)) {
+ if (ABSL_PREDICT_FALSE(*exp - 1 < float_traits.min_exponent)) {
+ *mantissa >>= (float_traits.min_exponent - *exp);
+ *exp = float_traits.min_exponent;
+ return;
+ }
+ *mantissa <<= 1;
+ --*exp;
+ }
+ // Extract bits for leading digit then shift them away leaving the
+ // fractional part.
+ *leading =
+ static_cast<uint8_t>(*mantissa >> (kIntBits - kLeadDigitBitsCount));
+ *exp -= (*mantissa != 0) ? kLeadDigitBitsCount : *exp;
+ *mantissa <<= kLeadDigitBitsCount;
+}
+
+template <typename Int>
+void FormatA(const HexFloatTypeParams float_traits, Int mantissa, int exp,
+ bool uppercase, const FormatState &state) {
+ // Int properties.
+ constexpr int kIntBits = sizeof(Int) * 8;
+ constexpr int kTotalNibbles = sizeof(Int) * 8 / 4;
+ // Did the user specify a precision explicitly?
+ const bool precision_specified = state.conv.precision() >= 0;
+
+ // ========== Normalize/Denormalize ==========
+ exp += kIntBits; // make all digits fractional digits.
+ // This holds the (up to four) bits of leading digit, i.e., the '1' in the
+ // number 0x1.e6fp+2. It's always > 0 unless number is zero or denormal.
+ uint8_t leading = 0;
+ FormatANormalize(float_traits, &leading, &mantissa, &exp);
+
+ // =============== Rounding ==================
+ // Check if we need to round; if so, then we do that by manipulating
+ // (incrementing) the mantissa before beginning to print characters.
+ FormatARound(precision_specified, state, &leading, &mantissa, &exp);
+
+ // ============= Format Result ===============
+ // This buffer holds the "0x1.ab1de3" portion of "0x1.ab1de3pe+2". Compute the
+ // size with long double which is the largest of the floats.
+ constexpr size_t kBufSizeForHexFloatRepr =
+ 2 // 0x
+ + std::numeric_limits<long double>::digits / 4 // number of hex digits
+ + 1 // round up
+ + 1; // "." (dot)
+ char digits_buffer[kBufSizeForHexFloatRepr];
+ char *digits_iter = digits_buffer;
+ const char *const digits =
+ static_cast<const char *>("0123456789ABCDEF0123456789abcdef") +
+ (uppercase ? 0 : 16);
+
+ // =============== Hex Prefix ================
+ *digits_iter++ = '0';
+ *digits_iter++ = uppercase ? 'X' : 'x';
+
+ // ========== Non-Fractional Digit ===========
+ *digits_iter++ = digits[leading];
+
+ // ================== Dot ====================
+ // There are three reasons we might need a dot. Keep in mind that, at this
+ // point, the mantissa holds only the fractional part.
+ if ((precision_specified && state.precision > 0) ||
+ (!precision_specified && mantissa > 0) || state.conv.has_alt_flag()) {
+ *digits_iter++ = '.';
+ }
+
+ // ============ Fractional Digits ============
+ int digits_emitted = 0;
+ while (mantissa > 0) {
+ *digits_iter++ = digits[GetNibble(mantissa, kTotalNibbles - 1)];
+ mantissa <<= 4;
+ ++digits_emitted;
+ }
+ int trailing_zeros =
+ precision_specified ? state.precision - digits_emitted : 0;
+ assert(trailing_zeros >= 0);
+ auto digits_result = string_view(digits_buffer, digits_iter - digits_buffer);
+
+ // =============== Exponent ==================
+ constexpr size_t kBufSizeForExpDecRepr =
+ numbers_internal::kFastToBufferSize // requred for FastIntToBuffer
+ + 1 // 'p' or 'P'
+ + 1; // '+' or '-'
+ char exp_buffer[kBufSizeForExpDecRepr];
+ exp_buffer[0] = uppercase ? 'P' : 'p';
+ exp_buffer[1] = exp >= 0 ? '+' : '-';
+ numbers_internal::FastIntToBuffer(exp < 0 ? -exp : exp, exp_buffer + 2);
+
+ // ============ Assemble Result ==============
+ FinalPrint(state, //
+ digits_result, // 0xN.NNN...
+ 2, // offset in `data` to start padding if needed.
+ trailing_zeros, // num remaining mantissa padding zeros
+ exp_buffer); // exponent
+}
+
char *CopyStringTo(absl::string_view v, char *out) {
std::memcpy(out, v.data(), v.size());
return out + v.size();
@@ -1103,7 +1361,10 @@ bool FloatToSink(const Float v, const FormatConversionSpecImpl &conv,
}
} else if (c == FormatConversionCharInternal::a ||
c == FormatConversionCharInternal::A) {
- return FallbackToSnprintf(v, conv, sink);
+ bool uppercase = (c == FormatConversionCharInternal::A);
+ FormatA(HexFloatTypeParams(Float{}), decomposed.mantissa,
+ decomposed.exponent, uppercase, {sign_char, precision, conv, sink});
+ return true;
} else {
return false;
}
diff --git a/absl/strings/str_cat.cc b/absl/strings/str_cat.cc
index d9afe2f3..dd5d25b0 100644
--- a/absl/strings/str_cat.cc
+++ b/absl/strings/str_cat.cc
@@ -141,12 +141,12 @@ namespace strings_internal {
std::string CatPieces(std::initializer_list<absl::string_view> pieces) {
std::string result;
size_t total_size = 0;
- for (const absl::string_view piece : pieces) total_size += piece.size();
+ for (const absl::string_view& piece : pieces) total_size += piece.size();
strings_internal::STLStringResizeUninitialized(&result, total_size);
char* const begin = &result[0];
char* out = begin;
- for (const absl::string_view piece : pieces) {
+ for (const absl::string_view& piece : pieces) {
const size_t this_size = piece.size();
if (this_size != 0) {
memcpy(out, piece.data(), this_size);
@@ -170,7 +170,7 @@ void AppendPieces(std::string* dest,
std::initializer_list<absl::string_view> pieces) {
size_t old_size = dest->size();
size_t total_size = old_size;
- for (const absl::string_view piece : pieces) {
+ for (const absl::string_view& piece : pieces) {
ASSERT_NO_OVERLAP(*dest, piece);
total_size += piece.size();
}
@@ -178,7 +178,7 @@ void AppendPieces(std::string* dest,
char* const begin = &(*dest)[0];
char* out = begin + old_size;
- for (const absl::string_view piece : pieces) {
+ for (const absl::string_view& piece : pieces) {
const size_t this_size = piece.size();
if (this_size != 0) {
memcpy(out, piece.data(), this_size);
generated by cgit v1.2.3 (git 2.39.1) at 2024-07-06 14:22:38 +0000