simplify exp

Author: tgross35

etc/update-api-list.py

@@ -3,6 +3,8 @@
 functions are covered by our macros.
 """
 
+# TOOD: also match with `${name}_any_suffix` so we pick up `fma_big`.
+
 import difflib
 import json
 import subprocess as sp

src/math/generic/fma.rs

@@ -1,7 +1,7 @@
 use super::super::fenv::{
     FE_INEXACT, FE_TONEAREST, FE_UNDERFLOW, feclearexcept, fegetround, feraiseexcept, fetestexcept,
 };
-use super::super::{CastFrom, CastInto, DFloat, Float, HFloat, IntTy, MinInt};
+use super::super::{CastFrom, CastInto, DFloat, Float, HFloat, Int, IntTy, MinInt};
 
 /// FMA implementation when a hardware-backed larger float type is available.
 pub fn fma_big<F, B>(x: F, y: F, z: F) -> F
@@ -23,7 +23,7 @@ where
     xy = x.widen() * y.widen();
     result = xy + z.widen();
     ui = result.to_bits();
-    e = i32::cast_from(ui >> F::SIG_BITS) & F::EXP_MAX as i32;
+    e = result.exp().signed();
     let zb: B = z.widen();
 
     let prec_diff = B::SIG_BITS - F::SIG_BITS;