Expand description
A 32-bit floating point type (specifically, the “binary32” type defined in IEEE 754-2008).
This type can represent a wide range of decimal numbers, like 3.5
, 27
,
-113.75
, 0.0078125
, 34359738368
, 0
, -1
. So unlike integer types
(such as i32
), floating point types can represent non-integer numbers,
too.
However, being able to represent this wide range of numbers comes at the
cost of precision: floats can only represent some of the real numbers and
calculation with floats round to a nearby representable number. For example,
5.0
and 1.0
can be exactly represented as f32
, but 1.0 / 5.0
results
in 0.20000000298023223876953125
since 0.2
cannot be exactly represented
as f32
. Note, however, that printing floats with println
and friends will
often discard insignificant digits: println!("{}", 1.0f32 / 5.0f32)
will
print 0.2
.
Additionally, f32
can represent some special values:
- −0.0: IEEE 754 floating point numbers have a bit that indicates their sign, so −0.0 is a possible value. For comparison −0.0 = +0.0, but floating point operations can carry the sign bit through arithmetic operations. This means −0.0 × +0.0 produces −0.0 and a negative number rounded to a value smaller than a float can represent also produces −0.0.
- ∞ and
−∞: these result from calculations
like
1.0 / 0.0
. - NaN (not a number): this value results from
calculations like
(-1.0).sqrt()
. NaN has some potentially unexpected behavior: it is unequal to any float, including itself! It is also neither smaller nor greater than any float, making it impossible to sort. Lastly, it is considered infectious as almost all calculations where one of the operands is NaN will also result in NaN.
For more information on floating point numbers, see Wikipedia.
Implementations
sourceimpl f32
impl f32
1.43.0 · sourcepub const MANTISSA_DIGITS: u32
pub const MANTISSA_DIGITS: u32
Number of significant digits in base 2.
1.43.0 · sourcepub const EPSILON: f32
pub const EPSILON: f32
Machine epsilon value for f32
.
This is the difference between 1.0
and the next larger representable number.
1.43.0 · sourcepub const MIN_POSITIVE: f32
pub const MIN_POSITIVE: f32
Smallest positive normal f32
value.
1.43.0 · sourcepub const MIN_EXP: i32
pub const MIN_EXP: i32
One greater than the minimum possible normal power of 2 exponent.
1.43.0 · sourcepub const MIN_10_EXP: i32
pub const MIN_10_EXP: i32
Minimum possible normal power of 10 exponent.
1.43.0 · sourcepub const MAX_10_EXP: i32
pub const MAX_10_EXP: i32
Maximum possible power of 10 exponent.
1.43.0 · sourcepub const NEG_INFINITY: f32
pub const NEG_INFINITY: f32
Negative infinity (−∞).
const: unstable · sourcepub fn is_nan(self) -> bool
pub fn is_nan(self) -> bool
Returns true
if this value is NaN
.
let nan = f32::NAN;
let f = 7.0_f32;
assert!(nan.is_nan());
assert!(!f.is_nan());
Runconst: unstable · sourcepub fn is_infinite(self) -> bool
pub fn is_infinite(self) -> bool
Returns true
if this value is positive infinity or negative infinity, and
false
otherwise.
let f = 7.0f32;
let inf = f32::INFINITY;
let neg_inf = f32::NEG_INFINITY;
let nan = f32::NAN;
assert!(!f.is_infinite());
assert!(!nan.is_infinite());
assert!(inf.is_infinite());
assert!(neg_inf.is_infinite());
Runconst: unstable · sourcepub fn is_finite(self) -> bool
pub fn is_finite(self) -> bool
Returns true
if this number is neither infinite nor NaN
.
let f = 7.0f32;
let inf = f32::INFINITY;
let neg_inf = f32::NEG_INFINITY;
let nan = f32::NAN;
assert!(f.is_finite());
assert!(!nan.is_finite());
assert!(!inf.is_finite());
assert!(!neg_inf.is_finite());
Run1.53.0 (const: unstable) · sourcepub fn is_subnormal(self) -> bool
pub fn is_subnormal(self) -> bool
Returns true
if the number is subnormal.
let min = f32::MIN_POSITIVE; // 1.17549435e-38f32
let max = f32::MAX;
let lower_than_min = 1.0e-40_f32;
let zero = 0.0_f32;
assert!(!min.is_subnormal());
assert!(!max.is_subnormal());
assert!(!zero.is_subnormal());
assert!(!f32::NAN.is_subnormal());
assert!(!f32::INFINITY.is_subnormal());
// Values between `0` and `min` are Subnormal.
assert!(lower_than_min.is_subnormal());
Runconst: unstable · sourcepub fn is_normal(self) -> bool
pub fn is_normal(self) -> bool
Returns true
if the number is neither zero, infinite,
subnormal, or NaN
.
let min = f32::MIN_POSITIVE; // 1.17549435e-38f32
let max = f32::MAX;
let lower_than_min = 1.0e-40_f32;
let zero = 0.0_f32;
assert!(min.is_normal());
assert!(max.is_normal());
assert!(!zero.is_normal());
assert!(!f32::NAN.is_normal());
assert!(!f32::INFINITY.is_normal());
// Values between `0` and `min` are Subnormal.
assert!(!lower_than_min.is_normal());
Runconst: unstable · sourcepub fn classify(self) -> FpCategory
pub fn classify(self) -> FpCategory
Returns the floating point category of the number. If only one property is going to be tested, it is generally faster to use the specific predicate instead.
use std::num::FpCategory;
let num = 12.4_f32;
let inf = f32::INFINITY;
assert_eq!(num.classify(), FpCategory::Normal);
assert_eq!(inf.classify(), FpCategory::Infinite);
Runconst: unstable · sourcepub fn is_sign_positive(self) -> bool
pub fn is_sign_positive(self) -> bool
Returns true
if self
has a positive sign, including +0.0
, NaN
s with
positive sign bit and positive infinity.
let f = 7.0_f32;
let g = -7.0_f32;
assert!(f.is_sign_positive());
assert!(!g.is_sign_positive());
Runconst: unstable · sourcepub fn is_sign_negative(self) -> bool
pub fn is_sign_negative(self) -> bool
Returns true
if self
has a negative sign, including -0.0
, NaN
s with
negative sign bit and negative infinity.
let f = 7.0f32;
let g = -7.0f32;
assert!(!f.is_sign_negative());
assert!(g.is_sign_negative());
Runsourcepub fn recip(self) -> f32
pub fn recip(self) -> f32
Takes the reciprocal (inverse) of a number, 1/x
.
let x = 2.0_f32;
let abs_difference = (x.recip() - (1.0 / x)).abs();
assert!(abs_difference <= f32::EPSILON);
Run1.7.0 · sourcepub fn to_degrees(self) -> f32
pub fn to_degrees(self) -> f32
Converts radians to degrees.
let angle = std::f32::consts::PI;
let abs_difference = (angle.to_degrees() - 180.0).abs();
assert!(abs_difference <= f32::EPSILON);
Run1.7.0 · sourcepub fn to_radians(self) -> f32
pub fn to_radians(self) -> f32
Converts degrees to radians.
let angle = 180.0f32;
let abs_difference = (angle.to_radians() - std::f32::consts::PI).abs();
assert!(abs_difference <= f32::EPSILON);
Runsourcepub fn max(self, other: f32) -> f32
pub fn max(self, other: f32) -> f32
Returns the maximum of the two numbers.
Follows the IEEE-754 2008 semantics for maxNum, except for handling of signaling NaNs. This matches the behavior of libm’s fmax.
let x = 1.0f32;
let y = 2.0f32;
assert_eq!(x.max(y), y);
RunIf one of the arguments is NaN, then the other argument is returned.
sourcepub fn min(self, other: f32) -> f32
pub fn min(self, other: f32) -> f32
Returns the minimum of the two numbers.
Follows the IEEE-754 2008 semantics for minNum, except for handling of signaling NaNs. This matches the behavior of libm’s fmin.
let x = 1.0f32;
let y = 2.0f32;
assert_eq!(x.min(y), x);
RunIf one of the arguments is NaN, then the other argument is returned.
sourcepub fn maximum(self, other: f32) -> f32
pub fn maximum(self, other: f32) -> f32
Returns the maximum of the two numbers, propagating NaNs.
This returns NaN when either argument is NaN, as opposed to
f32::max
which only returns NaN when both arguments are NaN.
#![feature(float_minimum_maximum)]
let x = 1.0f32;
let y = 2.0f32;
assert_eq!(x.maximum(y), y);
assert!(x.maximum(f32::NAN).is_nan());
RunIf one of the arguments is NaN, then NaN is returned. Otherwise this returns the greater of the two numbers. For this operation, -0.0 is considered to be less than +0.0. Note that this follows the semantics specified in IEEE 754-2019.
sourcepub fn minimum(self, other: f32) -> f32
pub fn minimum(self, other: f32) -> f32
Returns the minimum of the two numbers, propagating NaNs.
This returns NaN when either argument is NaN, as opposed to
f32::min
which only returns NaN when both arguments are NaN.
#![feature(float_minimum_maximum)]
let x = 1.0f32;
let y = 2.0f32;
assert_eq!(x.minimum(y), x);
assert!(x.minimum(f32::NAN).is_nan());
RunIf one of the arguments is NaN, then NaN is returned. Otherwise this returns the lesser of the two numbers. For this operation, -0.0 is considered to be less than +0.0. Note that this follows the semantics specified in IEEE 754-2019.
1.44.0 · sourcepub unsafe fn to_int_unchecked<Int>(self) -> Int where
Self: FloatToInt<Int>,
pub unsafe fn to_int_unchecked<Int>(self) -> Int where
Self: FloatToInt<Int>,
Rounds toward zero and converts to any primitive integer type, assuming that the value is finite and fits in that type.
let value = 4.6_f32;
let rounded = unsafe { value.to_int_unchecked::<u16>() };
assert_eq!(rounded, 4);
let value = -128.9_f32;
let rounded = unsafe { value.to_int_unchecked::<i8>() };
assert_eq!(rounded, i8::MIN);
RunSafety
The value must:
- Not be
NaN
- Not be infinite
- Be representable in the return type
Int
, after truncating off its fractional part
1.20.0 (const: unstable) · sourcepub fn to_bits(self) -> u32
pub fn to_bits(self) -> u32
Raw transmutation to u32
.
This is currently identical to transmute::<f32, u32>(self)
on all platforms.
See from_bits
for some discussion of the
portability of this operation (there are almost no issues).
Note that this function is distinct from as
casting, which attempts to
preserve the numeric value, and not the bitwise value.
Examples
assert_ne!((1f32).to_bits(), 1f32 as u32); // to_bits() is not casting!
assert_eq!((12.5f32).to_bits(), 0x41480000);
Run1.20.0 (const: unstable) · sourcepub fn from_bits(v: u32) -> Self
pub fn from_bits(v: u32) -> Self
Raw transmutation from u32
.
This is currently identical to transmute::<u32, f32>(v)
on all platforms.
It turns out this is incredibly portable, for two reasons:
- Floats and Ints have the same endianness on all supported platforms.
- IEEE-754 very precisely specifies the bit layout of floats.
However there is one caveat: prior to the 2008 version of IEEE-754, how to interpret the NaN signaling bit wasn’t actually specified. Most platforms (notably x86 and ARM) picked the interpretation that was ultimately standardized in 2008, but some didn’t (notably MIPS). As a result, all signaling NaNs on MIPS are quiet NaNs on x86, and vice-versa.
Rather than trying to preserve signaling-ness cross-platform, this implementation favors preserving the exact bits. This means that any payloads encoded in NaNs will be preserved even if the result of this method is sent over the network from an x86 machine to a MIPS one.
If the results of this method are only manipulated by the same architecture that produced them, then there is no portability concern.
If the input isn’t NaN, then there is no portability concern.
If you don’t care about signalingness (very likely), then there is no portability concern.
Note that this function is distinct from as
casting, which attempts to
preserve the numeric value, and not the bitwise value.
Examples
let v = f32::from_bits(0x41480000);
assert_eq!(v, 12.5);
Run1.40.0 (const: unstable) · sourcepub fn to_ne_bytes(self) -> [u8; 4]
pub fn to_ne_bytes(self) -> [u8; 4]
Return the memory representation of this floating point number as a byte array in native byte order.
As the target platform’s native endianness is used, portable code
should use to_be_bytes
or to_le_bytes
, as appropriate, instead.
Examples
let bytes = 12.5f32.to_ne_bytes();
assert_eq!(
bytes,
if cfg!(target_endian = "big") {
[0x41, 0x48, 0x00, 0x00]
} else {
[0x00, 0x00, 0x48, 0x41]
}
);
Run1.40.0 (const: unstable) · sourcepub fn from_ne_bytes(bytes: [u8; 4]) -> Self
pub fn from_ne_bytes(bytes: [u8; 4]) -> Self
Create a floating point value from its representation as a byte array in native endian.
As the target platform’s native endianness is used, portable code
likely wants to use from_be_bytes
or from_le_bytes
, as
appropriate instead.
Examples
let value = f32::from_ne_bytes(if cfg!(target_endian = "big") {
[0x41, 0x48, 0x00, 0x00]
} else {
[0x00, 0x00, 0x48, 0x41]
});
assert_eq!(value, 12.5);
Runsourcepub fn total_cmp(&self, other: &Self) -> Ordering
pub fn total_cmp(&self, other: &Self) -> Ordering
Return the ordering between self
and other
.
Unlike the standard partial comparison between floating point numbers,
this comparison always produces an ordering in accordance to
the totalOrder
predicate as defined in the IEEE 754 (2008 revision)
floating point standard. The values are ordered in the following sequence:
- negative quiet NaN
- negative signaling NaN
- negative infinity
- negative numbers
- negative subnormal numbers
- negative zero
- positive zero
- positive subnormal numbers
- positive numbers
- positive infinity
- positive signaling NaN
- positive quiet NaN.
The ordering established by this function does not always agree with the
PartialOrd
and PartialEq
implementations of f32
. For example,
they consider negative and positive zero equal, while total_cmp
doesn’t.
The interpretation of the signaling NaN bit follows the definition in the IEEE 754 standard, which may not match the interpretation by some of the older, non-conformant (e.g. MIPS) hardware implementations.
Example
#![feature(total_cmp)]
struct GoodBoy {
name: String,
weight: f32,
}
let mut bois = vec![
GoodBoy { name: "Pucci".to_owned(), weight: 0.1 },
GoodBoy { name: "Woofer".to_owned(), weight: 99.0 },
GoodBoy { name: "Yapper".to_owned(), weight: 10.0 },
GoodBoy { name: "Chonk".to_owned(), weight: f32::INFINITY },
GoodBoy { name: "Abs. Unit".to_owned(), weight: f32::NAN },
GoodBoy { name: "Floaty".to_owned(), weight: -5.0 },
];
bois.sort_by(|a, b| a.weight.total_cmp(&b.weight));
Run1.50.0 · sourcepub fn clamp(self, min: f32, max: f32) -> f32
pub fn clamp(self, min: f32, max: f32) -> f32
Restrict a value to a certain interval unless it is NaN.
Returns max
if self
is greater than max
, and min
if self
is
less than min
. Otherwise this returns self
.
Note that this function returns NaN if the initial value was NaN as well.
Panics
Panics if min > max
, min
is NaN, or max
is NaN.
Examples
assert!((-3.0f32).clamp(-2.0, 1.0) == -2.0);
assert!((0.0f32).clamp(-2.0, 1.0) == 0.0);
assert!((2.0f32).clamp(-2.0, 1.0) == 1.0);
assert!((f32::NAN).clamp(-2.0, 1.0).is_nan());
RunTrait Implementations
1.22.0 (const: unstable) · sourceimpl AddAssign<&'_ f32> for f32
impl AddAssign<&'_ f32> for f32
const: unstable · sourcefn add_assign(&mut self, other: &f32)
fn add_assign(&mut self, other: &f32)
Performs the +=
operation. Read more
1.8.0 (const: unstable) · sourceimpl AddAssign<f32> for f32
impl AddAssign<f32> for f32
const: unstable · sourcefn add_assign(&mut self, other: f32)
fn add_assign(&mut self, other: f32)
Performs the +=
operation. Read more
1.22.0 (const: unstable) · sourceimpl DivAssign<&'_ f32> for f32
impl DivAssign<&'_ f32> for f32
const: unstable · sourcefn div_assign(&mut self, other: &f32)
fn div_assign(&mut self, other: &f32)
Performs the /=
operation. Read more
1.8.0 (const: unstable) · sourceimpl DivAssign<f32> for f32
impl DivAssign<f32> for f32
const: unstable · sourcefn div_assign(&mut self, other: f32)
fn div_assign(&mut self, other: f32)
Performs the /=
operation. Read more
sourceimpl FromStr for f32
impl FromStr for f32
sourcefn from_str(src: &str) -> Result<Self, ParseFloatError>
fn from_str(src: &str) -> Result<Self, ParseFloatError>
Converts a string in base 10 to a float. Accepts an optional decimal exponent.
This function accepts strings such as
- ‘3.14’
- ‘-3.14’
- ‘2.5E10’, or equivalently, ‘2.5e10’
- ‘2.5E-10’
- ‘5.’
- ‘.5’, or, equivalently, ‘0.5’
- ‘inf’, ‘-inf’, ‘+infinity’, ‘NaN’
Note that alphabetical characters are not case-sensitive.
Leading and trailing whitespace represent an error.
Grammar
All strings that adhere to the following EBNF grammar when
lowercased will result in an Ok
being returned:
Float ::= Sign? ( 'inf' | 'infinity' | 'nan' | Number )
Number ::= ( Digit+ |
'.' Digit* |
Digit+ '.' Digit* |
Digit* '.' Digit+ ) Exp?
Exp ::= 'e' Sign? Digit+
Sign ::= [+-]
Digit ::= [0-9]
Arguments
- src - A string
Return value
Err(ParseFloatError)
if the string did not represent a valid
number. Otherwise, Ok(n)
where n
is the floating-point
number represented by src
.
type Err = ParseFloatError
type Err = ParseFloatError
The associated error which can be returned from parsing.
1.22.0 (const: unstable) · sourceimpl MulAssign<&'_ f32> for f32
impl MulAssign<&'_ f32> for f32
const: unstable · sourcefn mul_assign(&mut self, other: &f32)
fn mul_assign(&mut self, other: &f32)
Performs the *=
operation. Read more
1.8.0 (const: unstable) · sourceimpl MulAssign<f32> for f32
impl MulAssign<f32> for f32
const: unstable · sourcefn mul_assign(&mut self, other: f32)
fn mul_assign(&mut self, other: f32)
Performs the *=
operation. Read more
sourceimpl PartialOrd<f32> for f32
impl PartialOrd<f32> for f32
sourcefn partial_cmp(&self, other: &f32) -> Option<Ordering>
fn partial_cmp(&self, other: &f32) -> Option<Ordering>
This method returns an ordering between self
and other
values if one exists. Read more
sourcefn lt(&self, other: &f32) -> bool
fn lt(&self, other: &f32) -> bool
This method tests less than (for self
and other
) and is used by the <
operator. Read more
sourcefn le(&self, other: &f32) -> bool
fn le(&self, other: &f32) -> bool
This method tests less than or equal to (for self
and other
) and is used by the <=
operator. Read more
const: unstable · sourceimpl Rem<f32> for f32
impl Rem<f32> for f32
The remainder from the division of two floats.
The remainder has the same sign as the dividend and is computed as:
x - (x / y).trunc() * y
.
Examples
let x: f32 = 50.50;
let y: f32 = 8.125;
let remainder = x - (x / y).trunc() * y;
// The answer to both operations is 1.75
assert_eq!(x % y, remainder);
Run1.22.0 (const: unstable) · sourceimpl RemAssign<&'_ f32> for f32
impl RemAssign<&'_ f32> for f32
const: unstable · sourcefn rem_assign(&mut self, other: &f32)
fn rem_assign(&mut self, other: &f32)
Performs the %=
operation. Read more
1.8.0 (const: unstable) · sourceimpl RemAssign<f32> for f32
impl RemAssign<f32> for f32
const: unstable · sourcefn rem_assign(&mut self, other: f32)
fn rem_assign(&mut self, other: f32)
Performs the %=
operation. Read more
sourceimpl SimdElement for f32
impl SimdElement for f32
1.22.0 (const: unstable) · sourceimpl SubAssign<&'_ f32> for f32
impl SubAssign<&'_ f32> for f32
const: unstable · sourcefn sub_assign(&mut self, other: &f32)
fn sub_assign(&mut self, other: &f32)
Performs the -=
operation. Read more
1.8.0 (const: unstable) · sourceimpl SubAssign<f32> for f32
impl SubAssign<f32> for f32
const: unstable · sourcefn sub_assign(&mut self, other: f32)
fn sub_assign(&mut self, other: f32)
Performs the -=
operation. Read more