auto merge of #20573 : huonw/rust/num-stab-2, r=alexcrichton

cc #19260 

Open questions:

- I still feel weird about marking functions like `exp` as `#[stable]` in `core` since they're highly likely to call into libm which is theoretically something core is designed to avoid and so we may be forced/want to move it at some point in the future, and so it feels like a lie to call it `#[stable]` (I know `core` is `#[experimental]`, but still...)
- `abs_sub` is a horrible name IMO: it feels like it is `(a - b).abs()`, but it is actually `(a - b).max(0.)`. maybe something along the lines of `pos_diff` ("positive difference") is better.
- the associated-function nature of `Int::from_be` and `Int::from_le` feel strange to me, it feels like they should be methods, but I cannot think of a good name.

I'm also not hugely in favour of `ldexp` and `frexp` but the precedent from C is large. (e.g. AFAICT,  `ldexp` must mean "load exponent" which is essentially what it does... but only for a subset of its inputs.)

src/libcore/num/f32.rs

@@ -22,12 +22,12 @@ use num::Float;
 use num::FpCategory as Fp;
 use option::Option;
 
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const RADIX: uint = 2u;
 
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const MANTISSA_DIGITS: uint = 24u;
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const DIGITS: uint = 6u;
 
 #[stable]
@@ -43,14 +43,14 @@ pub const MIN_POS_VALUE: f32 = 1.17549435e-38_f32;
 #[stable]
 pub const MAX_VALUE: f32 = 3.40282347e+38_f32;
 
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const MIN_EXP: int = -125;
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const MAX_EXP: int = 128;
 
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const MIN_10_EXP: int = -37;
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const MAX_10_EXP: int = 38;
 
 #[stable]
@@ -177,33 +177,43 @@ impl Float for f32 {
     }
 
     #[inline]
+    #[deprecated]
     fn mantissa_digits(_: Option<f32>) -> uint { MANTISSA_DIGITS }
 
     #[inline]
+    #[deprecated]
     fn digits(_: Option<f32>) -> uint { DIGITS }
 
     #[inline]
+    #[deprecated]
     fn epsilon() -> f32 { EPSILON }
 
     #[inline]
+    #[deprecated]
     fn min_exp(_: Option<f32>) -> int { MIN_EXP }
 
     #[inline]
+    #[deprecated]
     fn max_exp(_: Option<f32>) -> int { MAX_EXP }
 
     #[inline]
+    #[deprecated]
     fn min_10_exp(_: Option<f32>) -> int { MIN_10_EXP }
 
     #[inline]
+    #[deprecated]
     fn max_10_exp(_: Option<f32>) -> int { MAX_10_EXP }
 
     #[inline]
+    #[deprecated]
     fn min_value() -> f32 { MIN_VALUE }
 
     #[inline]
+    #[deprecated]
     fn min_pos_value(_: Option<f32>) -> f32 { MIN_POS_VALUE }
 
     #[inline]
+    #[deprecated]
     fn max_value() -> f32 { MAX_VALUE }
 
     /// Returns the mantissa, exponent and sign as integers.

src/libcore/num/f64.rs

@@ -26,12 +26,11 @@ use option::Option;
 // constants are implemented in favour of referencing the respective
 // members of `Bounded` and `Float`.
 
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const RADIX: uint = 2u;
 
-#[stable]
 pub const MANTISSA_DIGITS: uint = 53u;
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const DIGITS: uint = 15u;
 
 #[stable]
@@ -47,14 +46,14 @@ pub const MIN_POS_VALUE: f64 = 2.2250738585072014e-308_f64;
 #[stable]
 pub const MAX_VALUE: f64 = 1.7976931348623157e+308_f64;
 
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const MIN_EXP: int = -1021;
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const MAX_EXP: int = 1024;
 
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const MIN_10_EXP: int = -307;
-#[stable]
+#[unstable = "pending integer conventions"]
 pub const MAX_10_EXP: int = 308;
 
 #[stable]
@@ -185,33 +184,43 @@ impl Float for f64 {
     }
 
     #[inline]
+    #[deprecated]
     fn mantissa_digits(_: Option<f64>) -> uint { MANTISSA_DIGITS }
 
     #[inline]
+    #[deprecated]
     fn digits(_: Option<f64>) -> uint { DIGITS }
 
     #[inline]
+    #[deprecated]
     fn epsilon() -> f64 { EPSILON }
 
     #[inline]
+    #[deprecated]
     fn min_exp(_: Option<f64>) -> int { MIN_EXP }
 
     #[inline]
+    #[deprecated]
     fn max_exp(_: Option<f64>) -> int { MAX_EXP }
 
     #[inline]
+    #[deprecated]
     fn min_10_exp(_: Option<f64>) -> int { MIN_10_EXP }
 
     #[inline]
+    #[deprecated]
     fn max_10_exp(_: Option<f64>) -> int { MAX_10_EXP }
 
     #[inline]
+    #[deprecated]
     fn min_value() -> f64 { MIN_VALUE }
 
     #[inline]
+    #[deprecated]
     fn min_pos_value(_: Option<f64>) -> f64 { MIN_POS_VALUE }
 
     #[inline]
+    #[deprecated]
     fn max_value() -> f64 { MAX_VALUE }
 
     /// Returns the mantissa, exponent and sign as integers.