Convert float_to_int! into a function

Author: est31

src/float/conv.rs

@@ -1,5 +1,5 @@
 use float::Float;
-use int::Int;
+use int::{Int, CastInto};
 
 macro_rules! int_to_float {
     ($i:expr, $ity:ty, $fty:ty) => ({
@@ -137,115 +137,116 @@ enum Sign {
     Negative
 }
 
-macro_rules! float_to_int {
-    ($f:expr, $fty:ty, $ity:ty) => ({
-        let f = $f;
-        let fixint_min = <$ity>::min_value();
-        let fixint_max = <$ity>::max_value();
-        let fixint_bits = <$ity>::BITS as usize;
-        let fixint_unsigned = fixint_min == 0;
-
-        let sign_bit = <$fty>::SIGN_MASK;
-        let significand_bits = <$fty>::SIGNIFICAND_BITS as usize;
-        let exponent_bias = <$fty>::EXPONENT_BIAS as usize;
-        //let exponent_max = <$fty>::exponent_max() as usize;
-
-        // Break a into sign, exponent, significand
-        let a_rep = <$fty>::repr(f);
-        let a_abs = a_rep & !sign_bit;
-
-        // this is used to work around -1 not being available for unsigned
-        let sign = if (a_rep & sign_bit) == 0 { Sign::Positive } else { Sign::Negative };
-        let mut exponent = (a_abs >> significand_bits) as usize;
-        let significand = (a_abs & <$fty>::SIGNIFICAND_MASK) | <$fty>::IMPLICIT_BIT;
-
-        // if < 1 or unsigned & negative
-        if  exponent < exponent_bias ||
-            fixint_unsigned && sign == Sign::Negative {
-            return 0
-        }
-        exponent -= exponent_bias;
-
-        // If the value is infinity, saturate.
-        // If the value is too large for the integer type, 0.
-        if exponent >= (if fixint_unsigned {fixint_bits} else {fixint_bits -1}) {
-            return if sign == Sign::Positive {fixint_max} else {fixint_min}
-        }
-        // If 0 <= exponent < significand_bits, right shift to get the result.
-        // Otherwise, shift left.
-        // (sign - 1) will never overflow as negative signs are already returned as 0 for unsigned
-        let r = if exponent < significand_bits {
-            (significand >> (significand_bits - exponent)) as $ity
-        } else {
-            (significand as $ity) << (exponent - significand_bits)
-        };
-
-        if sign == Sign::Negative {
-            (!r).wrapping_add(1)
-        } else {
-            r
-        }
-    })
+fn float_to_int<F: Float, I: Int>(f: F) -> I where
+    F::Int: CastInto<u32>,
+    F::Int: CastInto<I>,
+{
+    let f = f;
+    let fixint_min = I::min_value();
+    let fixint_max = I::max_value();
+    let fixint_bits = I::BITS;
+    let fixint_unsigned = fixint_min == I::ZERO;
+
+    let sign_bit = F::SIGN_MASK;
+    let significand_bits = F::SIGNIFICAND_BITS;
+    let exponent_bias = F::EXPONENT_BIAS;
+    //let exponent_max = F::exponent_max() as usize;
+
+    // Break a into sign, exponent, significand
+    let a_rep = F::repr(f);
+    let a_abs = a_rep & !sign_bit;
+
+    // this is used to work around -1 not being available for unsigned
+    let sign = if (a_rep & sign_bit) == F::Int::ZERO { Sign::Positive } else { Sign::Negative };
+    let mut exponent: u32 = (a_abs >> significand_bits).cast();
+    let significand = (a_abs & F::SIGNIFICAND_MASK) | F::IMPLICIT_BIT;
+
+    // if < 1 or unsigned & negative
+    if exponent < exponent_bias ||
+        fixint_unsigned && sign == Sign::Negative {
+        return I::ZERO;
+    }
+    exponent -= exponent_bias;
+
+    // If the value is infinity, saturate.
+    // If the value is too large for the integer type, 0.
+    if exponent >= (if fixint_unsigned {fixint_bits} else {fixint_bits -1}) {
+        return if sign == Sign::Positive {fixint_max} else {fixint_min}
+    }
+    // If 0 <= exponent < significand_bits, right shift to get the result.
+    // Otherwise, shift left.
+    // (sign - 1) will never overflow as negative signs are already returned as 0 for unsigned
+    let r: I = if exponent < significand_bits {
+        (significand >> (significand_bits - exponent)).cast()
+    } else {
+        (significand << (exponent - significand_bits)).cast()
+    };
+
+    if sign == Sign::Negative {
+        (!r).wrapping_add(I::ONE)
+    } else {
+        r
+    }
 }
 
 intrinsics! {
     #[arm_aeabi_alias = __aeabi_f2iz]
     pub extern "C" fn __fixsfsi(f: f32) -> i32 {
-        float_to_int!(f, f32, i32)
+        float_to_int(f)
     }
 
     #[arm_aeabi_alias = __aeabi_f2lz]
     pub extern "C" fn __fixsfdi(f: f32) -> i64 {
-        float_to_int!(f, f32, i64)
+        float_to_int(f)
     }
 
     #[unadjusted_on_win64]
     pub extern "C" fn __fixsfti(f: f32) -> i128 {
-        float_to_int!(f, f32, i128)
+        float_to_int(f)
     }
 
     #[arm_aeabi_alias = __aeabi_d2iz]
     pub extern "C" fn __fixdfsi(f: f64) -> i32 {
-        float_to_int!(f, f64, i32)
+        float_to_int(f)
     }
 
     #[arm_aeabi_alias = __aeabi_d2lz]
     pub extern "C" fn __fixdfdi(f: f64) -> i64 {
-        float_to_int!(f, f64, i64)
+        float_to_int(f)
     }
 
     #[unadjusted_on_win64]
     pub extern "C" fn __fixdfti(f: f64) -> i128 {
-        float_to_int!(f, f64, i128)
+        float_to_int(f)
     }
 
     #[arm_aeabi_alias = __aeabi_f2uiz]
     pub extern "C" fn __fixunssfsi(f: f32) -> u32 {
-        float_to_int!(f, f32, u32)
+        float_to_int(f)
     }
 
     #[arm_aeabi_alias = __aeabi_f2ulz]
     pub extern "C" fn __fixunssfdi(f: f32) -> u64 {
-        float_to_int!(f, f32, u64)
+        float_to_int(f)
     }
 
     #[unadjusted_on_win64]
     pub extern "C" fn __fixunssfti(f: f32) -> u128 {
-        float_to_int!(f, f32, u128)
+        float_to_int(f)
     }
 
     #[arm_aeabi_alias = __aeabi_d2uiz]
     pub extern "C" fn __fixunsdfsi(f: f64) -> u32 {
-        float_to_int!(f, f64, u32)
+        float_to_int(f)
     }
 
     #[arm_aeabi_alias = __aeabi_d2ulz]
     pub extern "C" fn __fixunsdfdi(f: f64) -> u64 {
-        float_to_int!(f, f64, u64)
+        float_to_int(f)
     }
 
     #[unadjusted_on_win64]
     pub extern "C" fn __fixunsdfti(f: f64) -> u128 {
-        float_to_int!(f, f64, u128)
+        float_to_int(f)
     }
 }

src/int/mod.rs

@@ -230,3 +230,28 @@ large_int!(u64, u32, u32, 32);
 large_int!(i64, u32, i32, 32);
 large_int!(u128, u64, u64, 64);
 large_int!(i128, u64, i64, 64);
+
+/// Trait to express (possibly lossy) casting of integers
+pub trait CastInto<T: Copy>: Copy {
+    fn cast(self) -> T;
+}
+
+macro_rules! cast_into {
+    ($ty:ty) => {
+        cast_into!($ty; usize, isize, u32, i32, u64, i64, u128, i128);
+    };
+    ($ty:ty; $($into:ty),*) => {$(
+        impl CastInto<$into> for $ty {
+            fn cast(self) -> $into {
+                self as $into
+            }
+        }
+    )*};
+}
+
+cast_into!(u32);
+cast_into!(i32);
+cast_into!(u64);
+cast_into!(i64);
+cast_into!(u128);
+cast_into!(i128);