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program format_49
! Test E format exponent adjustment when mantissa rounds to 0.999...
! Bug: exponent was off by one for extreme values like 1.0d-200
! when using high precision formats like E25.17
use, intrinsic :: iso_fortran_env, only: dp => real64
implicit none
real(dp) :: val
character(30) :: output
integer :: exp_val, i, exp_start
! 1.0d-200 with E25.17 format:
! Mantissa rounds to 0.99999999999999998
! So exponent must be -200 (not -199)
val = 1.0d-200
write(output, '(E25.17)') val
! Find the exponent sign position (last - or + in the string)
exp_start = 0
do i = len_trim(output), 1, -1
if (output(i:i) == '-' .or. output(i:i) == '+') then
exp_start = i
exit
end if
end do
! Parse exponent from the sign position
read(output(exp_start:), '(I4)') exp_val
if (exp_val /= -200) then
print *, "FAIL: 1.0d-200 exponent should be -200, got ", exp_val
print *, "Output was: ", trim(output)
error stop
end if
print *, "PASS: E format exponent correctly adjusted for 1.0d-200"
end program
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