Config Flag Lookup - Modern Fortran Programming

A small configuration table can store feature keys and on/off flags.

Program

Play the program to query a feature key and read the configured flag.

                            target_key
                            target_key = 2 (default)target_key = 1target_key = 4
                        

                            config_flag_lookup.f90
                        
Replay: real traced execution (multi-file project)

                            program config_flag_lookup_demo
    implicit none
    integer :: keys(3)
    integer :: enabled(3)
    integer :: target_key
    integer :: i
    integer :: flag

    keys = [1, 2, 3]
    enabled = [1, 0, 1]
    target_key = 2
    flag = 0
    do i = 1, 3
        if (keys(i) == target_key) flag = enabled(i)
    end do
    print '(I0, 1X, I0)', target_key, flag
end program config_flag_lookup_demo
program config_flag_lookup_demo
    implicit none
    integer :: keys(3)
    integer :: enabled(3)
    integer :: target_key
    integer :: i
    integer :: flag

    keys = [1, 2, 3]
    enabled = [1, 0, 1]
    target_key = 1
    flag = 0
    do i = 1, 3
        if (keys(i) == target_key) flag = enabled(i)
    end do
    print '(I0, 1X, I0)', target_key, flag
end program config_flag_lookup_demo
program config_flag_lookup_demo
    implicit none
    integer :: keys(3)
    integer :: enabled(3)
    integer :: target_key
    integer :: i
    integer :: flag

    keys = [1, 2, 3]
    enabled = [1, 0, 1]
    target_key = 4
    flag = 0
    do i = 1, 3
        if (keys(i) == target_key) flag = enabled(i)
    end do
    print '(I0, 1X, I0)', target_key, flag
end program config_flag_lookup_demo

                        
1keys ← [1, 2, 3]⋯9keys = [1, 2, 3]10enabled = [1, 0, 1]⋯values this step[1, 2, 3]keys
2enabled ← [1, 0, 1]⋯9keys = [1, 2, 3]10enabled = [1, 0, 1]11target_key = 2⋯values this step[1, 0, 1]enabled
3target_key ← 2⋯10enabled = [1, 0, 1]11target_key = 212flag = 0⋯values this step2target_key
4flag ← 0⋯11target_key = 212flag = 013do i = 1, 3⋯values this step0flag
5i ← 1⋯12flag = 013do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)⋯values this step1i
6if (keys(i) == target_key) flag = enabled(i)⋯13do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)15end do⋯values this step.false.keys(1) == target_key
7i ← 2⋯12flag = 013do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)⋯values this step2i
8flag ← 0⋯13do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)15end do⋯values this step0flag.true.keys(2) == target_key
9i ← 3⋯12flag = 013do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)⋯values this step3i
10if (keys(i) == target_key) flag = enabled(i)⋯13do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)15end do⋯values this step.false.keys(3) == target_key
11print '(I0, 1X, I0)', target_key, flag⋯15    end do16    print '(I0, 1X, I0)', target_key, flag17end program config_flag_lookup_demooutput2 0values this step2target_key0flag
1keys ← [1, 2, 3]⋯9keys = [1, 2, 3]10enabled = [1, 0, 1]⋯values this step[1, 2, 3]keys
2enabled ← [1, 0, 1]⋯9keys = [1, 2, 3]10enabled = [1, 0, 1]11target_key = 1⋯values this step[1, 0, 1]enabled
3target_key ← 1⋯10enabled = [1, 0, 1]11target_key = 112flag = 0⋯values this step1target_key
4flag ← 0⋯11target_key = 112flag = 013do i = 1, 3⋯values this step0flag
5i ← 1⋯12flag = 013do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)⋯values this step1i
6flag ← 1⋯13do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)15end do⋯values this step1flag.true.keys(1) == target_key
7i ← 2⋯12flag = 013do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)⋯values this step2i
8if (keys(i) == target_key) flag = enabled(i)⋯13do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)15end do⋯values this step.false.keys(2) == target_key
9i ← 3⋯12flag = 013do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)⋯values this step3i
10if (keys(i) == target_key) flag = enabled(i)⋯13do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)15end do⋯values this step.false.keys(3) == target_key
11print '(I0, 1X, I0)', target_key, flag⋯15    end do16    print '(I0, 1X, I0)', target_key, flag17end program config_flag_lookup_demooutput1 1values this step1target_key1flag
1keys ← [1, 2, 3]⋯9keys = [1, 2, 3]10enabled = [1, 0, 1]⋯values this step[1, 2, 3]keys
2enabled ← [1, 0, 1]⋯9keys = [1, 2, 3]10enabled = [1, 0, 1]11target_key = 4⋯values this step[1, 0, 1]enabled
3target_key ← 4⋯10enabled = [1, 0, 1]11target_key = 412flag = 0⋯values this step4target_key
4flag ← 0⋯11target_key = 412flag = 013do i = 1, 3⋯values this step0flag
5i ← 1⋯12flag = 013do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)⋯values this step1i
6if (keys(i) == target_key) flag = enabled(i)⋯13do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)15end do⋯values this step.false.keys(1) == target_key
7i ← 2⋯12flag = 013do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)⋯values this step2i
8if (keys(i) == target_key) flag = enabled(i)⋯13do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)15end do⋯values this step.false.keys(2) == target_key
9i ← 3⋯12flag = 013do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)⋯values this step3i
10if (keys(i) == target_key) flag = enabled(i)⋯13do i = 1, 314    if (keys(i) == target_key) flag = enabled(i)15end do⋯values this step.false.keys(3) == target_key
11print '(I0, 1X, I0)', target_key, flag⋯15    end do16    print '(I0, 1X, I0)', target_key, flag17end program config_flag_lookup_demooutput4 0values this step4target_key0flag

Follow the Lookup

keys is [1, 2, 3].
enabled is [1, 0, 1].
target_key starts at 2.
flag starts at 0, then the loop checks each key.
Key 2 matches row 2, so flag becomes 0 and the program prints 2 0. | target_key | matching row | enabled value | output | | ---: | --- | ---: | --- | | 1 | row 1 | 1 | 1 1 | | 2 | row 2 | 0 | 2 0 | | 4 | none | 0 | 4 0 |

feature key `target_key` chooses which setting row to read.

flag table `enabled` stores compact integer flags for the feature rows.

missing default `flag` starts at zero, so unknown keys stay disabled.

Exercise: config_flag_lookup.f90

Reproduce 2 0, then use target_key 1 and 4 to predict 1 1 and 4 0.