[GitHub] [incubator-nuttx] nealef commented on a diff in pull request #7025: Add check in roundx() functions for infinite or NaN cases

[GitBox]

nealef commented on code in PR #7025:
URL: https://github.com/apache/incubator-nuttx/pull/7025#discussion_r964342540


##########
libs/libc/math/lib_roundl.c:
##########
@@ -34,6 +34,9 @@
 #ifdef CONFIG_HAVE_LONG_DOUBLE
 long double roundl(long double x)
 {
+  if (isinf(x) || isnan(x))

Review Comment:
   I'm not sure it's needed unlike float, where infinity/nan are not just 
truncated versions of the double value, they have different values:
   
   #### long double
   - infinity: 0x7fff000000000000 0000000000000000 
   - nan: 0x7fff800000000000 0000000000000000
   
   #### double
   - infinity: 0x7fff000000000000 
   - nan: 0x7fff800000000000 
   
   #### float
   - infinity: 0x7f800000 
   - nan: 0x7fc00000  
   
   If you are using `gcc` you can use `__builtin_infl()`, `__builtin_inf()`, 
`__builtin_inff()`, `__builtin_nanl("")`, `__builtin_nan("")`, and 
`__builtin_nanf("")`. 
   
   However, reusing `INFINITY` and `NAN` for long doubles is fine from a value 
perspective.



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