1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
use crate::fmt::{Debug, Display, Formatter, LowerExp, Result, UpperExp};
use crate::mem::MaybeUninit;
use crate::num::{flt2dec, fmt as numfmt};

#[doc(hidden)]
trait GeneralFormat: PartialOrd {
    /// Determines if a value should use exponential based on its magnitude, given the precondition
    /// that it will not be rounded any further before it is displayed.
    fn already_rounded_value_should_use_exponential(&self) -> bool;
}

macro_rules! impl_general_format {
    ($($t:ident)*) => {
        $(impl GeneralFormat for $t {
            fn already_rounded_value_should_use_exponential(&self) -> bool {
                let abs = $t::abs_private(*self);
                (abs != 0.0 && abs < 1e-4) || abs >= 1e+16
            }
        })*
    }
}

impl_general_format! { f32 f64 }

// Don't inline this so callers don't use the stack space this function
// requires unless they have to.
#[inline(never)]
fn float_to_decimal_common_exact<T>(
    fmt: &mut Formatter<'_>,
    num: &T,
    sign: flt2dec::Sign,
    precision: usize,
) -> Result
where
    T: flt2dec::DecodableFloat,
{
    let mut buf: [MaybeUninit<u8>; 1024] = [MaybeUninit::uninit(); 1024]; // enough for f32 and f64
    let mut parts: [MaybeUninit<numfmt::Part<'_>>; 4] = [MaybeUninit::uninit(); 4];
    let formatted = flt2dec::to_exact_fixed_str(
        flt2dec::strategy::grisu::format_exact,
        *num,
        sign,
        precision,
        &mut buf,
        &mut parts,
    );
    // SAFETY: `to_exact_fixed_str` and `format_exact` produce only ASCII characters.
    unsafe { fmt.pad_formatted_parts(&formatted) }
}

// Don't inline this so callers that call both this and the above won't wind
// up using the combined stack space of both functions in some cases.
#[inline(never)]
fn float_to_decimal_common_shortest<T>(
    fmt: &mut Formatter<'_>,
    num: &T,
    sign: flt2dec::Sign,
    precision: usize,
) -> Result
where
    T: flt2dec::DecodableFloat,
{
    // enough for f32 and f64
    let mut buf: [MaybeUninit<u8>; flt2dec::MAX_SIG_DIGITS] =
        [MaybeUninit::uninit(); flt2dec::MAX_SIG_DIGITS];
    let mut parts: [MaybeUninit<numfmt::Part<'_>>; 4] = [MaybeUninit::uninit(); 4];
    let formatted = flt2dec::to_shortest_str(
        flt2dec::strategy::grisu::format_shortest,
        *num,
        sign,
        precision,
        &mut buf,
        &mut parts,
    );
    // SAFETY: `to_shortest_str` and `format_shortest` produce only ASCII characters.
    unsafe { fmt.pad_formatted_parts(&formatted) }
}

fn float_to_decimal_display<T>(fmt: &mut Formatter<'_>, num: &T) -> Result
where
    T: flt2dec::DecodableFloat,
{
    let force_sign = fmt.sign_plus();
    let sign = match force_sign {
        false => flt2dec::Sign::Minus,
        true => flt2dec::Sign::MinusPlus,
    };

    if let Some(precision) = fmt.precision {
        float_to_decimal_common_exact(fmt, num, sign, precision)
    } else {
        let min_precision = 0;
        float_to_decimal_common_shortest(fmt, num, sign, min_precision)
    }
}

// Don't inline this so callers don't use the stack space this function
// requires unless they have to.
#[inline(never)]
fn float_to_exponential_common_exact<T>(
    fmt: &mut Formatter<'_>,
    num: &T,
    sign: flt2dec::Sign,
    precision: usize,
    upper: bool,
) -> Result
where
    T: flt2dec::DecodableFloat,
{
    let mut buf: [MaybeUninit<u8>; 1024] = [MaybeUninit::uninit(); 1024]; // enough for f32 and f64
    let mut parts: [MaybeUninit<numfmt::Part<'_>>; 6] = [MaybeUninit::uninit(); 6];
    let formatted = flt2dec::to_exact_exp_str(
        flt2dec::strategy::grisu::format_exact,
        *num,
        sign,
        precision,
        upper,
        &mut buf,
        &mut parts,
    );
    // SAFETY: `to_exact_exp_str` and `format_exact` produce only ASCII characters.
    unsafe { fmt.pad_formatted_parts(&formatted) }
}

// Don't inline this so callers that call both this and the above won't wind
// up using the combined stack space of both functions in some cases.
#[inline(never)]
fn float_to_exponential_common_shortest<T>(
    fmt: &mut Formatter<'_>,
    num: &T,
    sign: flt2dec::Sign,
    upper: bool,
) -> Result
where
    T: flt2dec::DecodableFloat,
{
    // enough for f32 and f64
    let mut buf: [MaybeUninit<u8>; flt2dec::MAX_SIG_DIGITS] =
        [MaybeUninit::uninit(); flt2dec::MAX_SIG_DIGITS];
    let mut parts: [MaybeUninit<numfmt::Part<'_>>; 6] = [MaybeUninit::uninit(); 6];
    let formatted = flt2dec::to_shortest_exp_str(
        flt2dec::strategy::grisu::format_shortest,
        *num,
        sign,
        (0, 0),
        upper,
        &mut buf,
        &mut parts,
    );
    // SAFETY: `to_shortest_exp_str` and `format_shortest` produce only ASCII characters.
    unsafe { fmt.pad_formatted_parts(&formatted) }
}

// Common code of floating point LowerExp and UpperExp.
fn float_to_exponential_common<T>(fmt: &mut Formatter<'_>, num: &T, upper: bool) -> Result
where
    T: flt2dec::DecodableFloat,
{
    let force_sign = fmt.sign_plus();
    let sign = match force_sign {
        false => flt2dec::Sign::Minus,
        true => flt2dec::Sign::MinusPlus,
    };

    if let Some(precision) = fmt.precision {
        // 1 integral digit + `precision` fractional digits = `precision + 1` total digits
        float_to_exponential_common_exact(fmt, num, sign, precision + 1, upper)
    } else {
        float_to_exponential_common_shortest(fmt, num, sign, upper)
    }
}

fn float_to_general_debug<T>(fmt: &mut Formatter<'_>, num: &T) -> Result
where
    T: flt2dec::DecodableFloat + GeneralFormat,
{
    let force_sign = fmt.sign_plus();
    let sign = match force_sign {
        false => flt2dec::Sign::Minus,
        true => flt2dec::Sign::MinusPlus,
    };

    if let Some(precision) = fmt.precision {
        // this behavior of {:.PREC?} predates exponential formatting for {:?}
        float_to_decimal_common_exact(fmt, num, sign, precision)
    } else {
        // since there is no precision, there will be no rounding
        if num.already_rounded_value_should_use_exponential() {
            let upper = false;
            float_to_exponential_common_shortest(fmt, num, sign, upper)
        } else {
            let min_precision = 1;
            float_to_decimal_common_shortest(fmt, num, sign, min_precision)
        }
    }
}

macro_rules! floating {
    ($ty:ident) => {
        #[stable(feature = "rust1", since = "1.0.0")]
        impl Debug for $ty {
            fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
                float_to_general_debug(fmt, self)
            }
        }

        #[stable(feature = "rust1", since = "1.0.0")]
        impl Display for $ty {
            fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
                float_to_decimal_display(fmt, self)
            }
        }

        #[stable(feature = "rust1", since = "1.0.0")]
        impl LowerExp for $ty {
            fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
                float_to_exponential_common(fmt, self, false)
            }
        }

        #[stable(feature = "rust1", since = "1.0.0")]
        impl UpperExp for $ty {
            fn fmt(&self, fmt: &mut Formatter<'_>) -> Result {
                float_to_exponential_common(fmt, self, true)
            }
        }
    };
}

floating! { f32 }
floating! { f64 }

#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for f16 {
    #[inline]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        write!(f, "{:#06x}", self.to_bits())
    }
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Debug for f128 {
    #[inline]
    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
        write!(f, "{:#034x}", self.to_bits())
    }
}