SDK Question - Match Total Exposure

Match Total Exposures adjusts the target photo's Exposure develop setting so that its effective exposure value is the same as that of the source photo.  Below is the code my Any Filter plugin uses for computing exposure value (EV) and effective exposure value.  You can get the shutter speed, aperture, and ISO using photo:getRawMetadata().

--[[----------------------------------------------------------------------------
public number 
ev (number shutterSpeed, number aperture, number iso)

Returns the exposure value of the shutterSpeed, aperture, and iso, or nil
if any one of them is nil.
------------------------------------------------------------------------------]]

function ExposureValue.ev (es, shutterSpeed, aperture, iso) 
    return (shutterSpeed and aperture and iso) and 
        log2 (aperture ^ 2 / shutterSpeed) - log2 (iso / 100) or nil
    end
    
--[[----------------------------------------------------------------------------
public number 
effectiveEV (number shutterSpeed, number aperture, number iso, 
    string processVersion, number exposure2012, number exposure)

Returns the effective exposure value, taking into account the additional
stops of the Develop setting "exposure2012" (if "processVersion" is "6.7")
or "exposure" (if "processVersion" is earlier).  Returns nil if any of the
arguments actually used to compute effective EV are nil.
------------------------------------------------------------------------------]]

function ExposureValue.effectiveEV (es, shutterSpeed, aperture, iso, 
        processVersion, exposure2012, exposure) 
    local processVersionNum = tonumber (processVersion) or 0
    local exp = processVersionNum >= 6.7 and exposure2012 or exposure
    return (shutterSpeed and aperture and iso and exp) and 
        ExposureValue.ev (es, shutterSpeed, aperture, iso) - exp or nil
    end