https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102860
--- Comment #6 from luoxhu at gcc dot gnu.org --- Fortran's modulo is floor_mod as documented here: https://gcc.gnu.org/onlinedocs/gfortran/MODULO.html? Syntax: RESULT = MODULO(A, P) Return value: The type and kind of the result are those of the arguments. (As a GNU extension, kind is the largest kind of the actual arguments.) If A and P are of type INTEGER: MODULO(A,P) has the value R such that A=Q*P+R, where Q is an integer and R is between 0 (inclusive) and P (exclusive). If A and P are of type REAL: MODULO(A,P) has the value of A - FLOOR (A / P) * P. The returned value has the same sign as P and a magnitude less than the magnitude of P. program test_modulo print *, modulo(17,3) print *, modulo(17.5,5.5) print *, modulo(-17,3) print *, modulo(-17.5,5.5) print *, modulo(17,-3) print *, modulo(17.5,-5.5) end program LD_LIBRARY_PATH=./x86_64-pc-linux-gnu/libgfortran/.libs/ ./a.out 2 1.00000000 1 4.50000000 -1 -4.50000000
