Rollup merge of #124609 - RalfJung:float-precision, r=cuviper

variable-precision float operations can differ depending on optimization levels

Follow-up to #121793 and #118217 that accounts for optimizations changing the precision of these functions.

Fixes #109118
Fixes #71355

Author: matthiaskrgr

library/std/src/f32.rs

@@ -371,9 +371,10 @@ impl f32 {
     /// It might have a different sequence of rounding operations than `powf`,
     /// so the results are not guaranteed to agree.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -393,9 +394,10 @@ impl f32 {
 
     /// Raises a number to a floating point power.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -444,9 +446,10 @@ impl f32 {
 
     /// Returns `e^(self)`, (the exponential function).
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -470,9 +473,10 @@ impl f32 {
 
     /// Returns `2^(self)`.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -494,9 +498,10 @@ impl f32 {
 
     /// Returns the natural logarithm of the number.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -524,9 +529,10 @@ impl f32 {
     /// `self.log2()` can produce more accurate results for base 2, and
     /// `self.log10()` can produce more accurate results for base 10.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -548,9 +554,10 @@ impl f32 {
 
     /// Returns the base 2 logarithm of the number.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -572,9 +579,10 @@ impl f32 {
 
     /// Returns the base 10 logarithm of the number.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -599,9 +607,10 @@ impl f32 {
     /// * If `self <= other`: `0.0`
     /// * Else: `self - other`
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `fdimf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -637,9 +646,10 @@ impl f32 {
 
     /// Returns the cube root of a number.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `cbrtf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -666,9 +676,10 @@ impl f32 {
     /// right-angle triangle with other sides having length `x.abs()` and
     /// `y.abs()`.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `hypotf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -693,9 +704,10 @@ impl f32 {
 
     /// Computes the sine of a number (in radians).
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -716,9 +728,10 @@ impl f32 {
 
     /// Computes the cosine of a number (in radians).
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -739,9 +752,10 @@ impl f32 {
 
     /// Computes the tangent of a number (in radians).
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `tanf` from libc on Unix and
     /// Windows. Note that this might change in the future.
     ///
@@ -765,9 +779,10 @@ impl f32 {
     /// the range [-pi/2, pi/2] or NaN if the number is outside the range
     /// [-1, 1].
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `asinf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -794,9 +809,10 @@ impl f32 {
     /// the range [0, pi] or NaN if the number is outside the range
     /// [-1, 1].
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `acosf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -822,9 +838,10 @@ impl f32 {
     /// Computes the arctangent of a number. Return value is in radians in the
     /// range [-pi/2, pi/2];
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `atanf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -854,9 +871,10 @@ impl f32 {
     /// * `y >= 0`: `arctan(y/x) + pi` -> `(pi/2, pi]`
     /// * `y < 0`: `arctan(y/x) - pi` -> `(-pi, -pi/2)`
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `atan2f` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -890,9 +908,10 @@ impl f32 {
     /// Simultaneously computes the sine and cosine of the number, `x`. Returns
     /// `(sin(x), cos(x))`.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `(f32::sin(x),
     /// f32::cos(x))`. Note that this might change in the future.
     ///
@@ -919,9 +938,10 @@ impl f32 {
     /// Returns `e^(self) - 1` in a way that is accurate even if the
     /// number is close to zero.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `expm1f` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -947,9 +967,10 @@ impl f32 {
     /// Returns `ln(1+n)` (natural logarithm) more accurately than if
     /// the operations were performed separately.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `log1pf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -975,9 +996,10 @@ impl f32 {
 
     /// Hyperbolic sine function.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `sinhf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -1004,9 +1026,10 @@ impl f32 {
 
     /// Hyperbolic cosine function.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `coshf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -1033,9 +1056,10 @@ impl f32 {
 
     /// Hyperbolic tangent function.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `tanhf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -1062,9 +1086,10 @@ impl f32 {
 
     /// Inverse hyperbolic sine function.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -1089,9 +1114,10 @@ impl f32 {
 
     /// Inverse hyperbolic cosine function.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -1118,9 +1144,10 @@ impl f32 {
 
     /// Inverse hyperbolic tangent function.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     ///
     /// # Examples
     ///
@@ -1143,9 +1170,10 @@ impl f32 {
 
     /// Gamma function.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `tgammaf` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///
@@ -1171,9 +1199,10 @@ impl f32 {
     ///
     /// The integer part of the tuple indicates the sign of the gamma function.
     ///
-    /// # Platform-specific precision
+    /// # Unspecified precision
     ///
-    /// The precision of this function varies by platform and Rust version.
+    /// The precision of this function is non-deterministic. This means it varies by platform, Rust version, and
+    /// can even differ within the same execution from one invocation to the next.
     /// This function currently corresponds to the `lgamma_r` from libc on Unix
     /// and Windows. Note that this might change in the future.
     ///