About the REAL constants in iso_fortran_env

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REAL128 specifies, according to the standard, "a REAL type whose storage size expressed in bits is 128”.
On x86_64-linux, the storage size of both extended-precision (kind=10) and quadruple precision (kind=16) is equal to 128 bits. Both 10 and 16 are thus valid values for REAL128.

Check the comp.lang.fortran thread over there:
https://groups.google.com/forum/#!searchin/comp.lang.fortran/"real128"$20"iso_fortran_env"|sort:date/comp.lang.fortran/ThADTdybGmA/CePXaAoePz4J

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