[libc-commits] [PATCH] D136699: [libc] tighten strtofloat cutoffs

[Siva Chandra via Phabricator via libc-commits]

sivachandra accepted this revision.
sivachandra added inline comments.
This revision is now accepted and ready to land.


================
Comment at: libc/src/__support/str_to_float.h:563
+// give a non-zero result for this size of float. The value is
+// log_10(2^(exponent bias + mantissa width + intermediate mantissa width))
+// The generic approximation uses the fact that log_10(2^x) ~= x/3
----------------
What is "intermediate mantissa width"?


================
Comment at: libc/src/__support/str_to_float.h:600
   // If the exponent is too small even for a subnormal, return 0.
-  if (exp10 < 0 &&
-      -static_cast<int64_t>(exp10) >
-          static_cast<int64_t>(fputil::FloatProperties<T>::EXPONENT_BIAS +
-                               fputil::FloatProperties<T>::MANTISSA_WIDTH) /
-              2) {
+  if (exp10 < 0 && -static_cast<int64_t>(exp10) > get_lower_bound<T>()) {
     *outputMantissa = 0;
----------------
If you return a negative value from `get_lower_bound`, you don't have to do the inverted test, but simply:

```
if (exp10 < 0 && int64_t(exp) < get_lower_bound<T>()) {
  ...
}
```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D136699/new/

https://reviews.llvm.org/D136699