Formatted value-error string

•print ValueErrorString(12.34e-5, 1.11e-5) + "V"
  0.12(1) mV
•print ValueErrorString(12.34e-5, 1.11e-5, delta=1e-6, format="v(±e)") + "F"
  123(±11)µF
•print ValueErrorString(12.34e-5, 1.11e-5, delta=1e-7, format="(v ± e) ") + "T"
  (123.4 ± 11.1) µT

// function/S ValueErrorString(value, error, [delta, format, expformat, nonmetric]) 
//  returns a formatted value-error string terminating with a metric prefix
//  intended use is with properly "dimensioned" quantities, see examples
//
//  Examples:
//  •print ValueErrorString(12.34e-5, 1.11e-5) + "V"
//    0.12(1) mV
//  •print ValueErrorString(12.34e-5, 1.11e-5, delta=1e-6, format="v(±e)") + "F"
//    123(±11)µF
//  •print ValueErrorString(12.34e-5, 1.11e-5, delta=1e-7, format="(v ± e) ") + "T"
//    (123.4 ± 11.1) µT
//
//  Required parameters:    
//  variable value, error
//
//  Optional parameters:
//  variable delta (default: delta = error) -- the smallest distinguishable increment
//      this influences how many significant digits will be returned in the output (see examples)
//  string format (default: "v(e) ") -- format of value and error
//      "v" and "e" (must be small letters) are placeholders for value and error
//      if "v" is missing, output will start with value, followed by the rest of whatever you pass for format
//      if "e" is missing, "(±e) " will be appended next, then the exponential prefix (see below)
//          thus, if you say  format = " ", you'll get the format "v (±e) "
//      spaces and brackets are allowed and will appear in the output as expected
//  string expformat (default: "x 10\S%d\M ") -- format of exponential prefix if not metric
//      normally, a metric prefix is appended as appropriate (e.g., "µ" for 10^(-6))
//      the prefix is chosen such that no trailing zeroes occur in most cases (see examples)
//      if the value is outside of the range of WM prefixes "TGMk.mµnpf", the prefix is a number.
//          the default "x 10\S%d\M " is useful for Annotations etc. with formatted text
//          the prefix value is then floor(log(abs(value))) (i.e., 20 for value=3.45e20)
//      if you override the default, use %d or %+d as a placeholder for the exponent
//          "E%d" will give E20 or E-20 if the exponent is +20 or -20.
//          "E%+d" will give E+20 or E-20 if the exponent is +20 or -20.
//  variable nonmetric (default = 0) -- set to non-zero value to suppress metric prefixes
//
function/S ValueErrorString(value, error, [delta, format, expformat, nonmetric])
variable value, error, delta
string format, expformat
variable nonmetric
 
// set defaults for possibly missing parameters
    if( ParamIsDefault(delta) )
        delta = error
    endif
    if( ParamIsDefault(format) )
        format = "v(e) "
    endif
    if( ParamIsDefault(expformat) )
        expformat = "x 10\S%d\M "
    endif
    if( ParamIsDefault(nonmetric) )
        nonmetric = 0
    endif
    
// calculate and preformat exponent
    variable prec = floor(log(abs(delta))), eng = ceil(prec/3), digits
    string pref, result
    if( nonmetric || (eng < -5) || (eng > 4) )
        variable prec1 = floor(log(abs(value))) // added to give normal form n.nnn(nn) Enn
        sprintf pref, expformat, prec1
        eng = prec1 / 3
        digits = prec1 - prec
    else
        pref = "fpnµm.kMGT"[5+eng]
        if( !cmpstr(pref, ".") )
            pref = ""
        endif
        digits = 3*eng - prec
    endif
    value *= 10^(-3*eng)
    error *= 10^(-3*eng)
    string digstr = num2istr(digits)
    
// parse format, set defaults
    if( strsearch(format, "v", 0) < 0 )
        format = "v" + format
    endif
    if( strsearch(format, "e", 0) < 0 )
        format += "(±e) "
    endif
 
// print value
    format = ReplaceString("v", format, "%."+digstr+"f")
    
// case 1: error is non-zero (full format)
    if( error != 0 )
        if( strsearch(format, "±", 0) < 0 )    // special error format, zap zeros
            format = ReplaceString("e", format, "@%."+digstr+"f@")  // mark error value with "@"
        else
            format = ReplaceString("e", format, "%."+digstr+"f")
        endif
        format += "%s"
// print whole string
        sprintf result, format, value, error, pref
        
// treat special error format: zap leading zeros, including possible decimal point
        variable errpos = strsearch(result, "@", 0), nextchar
        if( errpos >= 0 )
            do
                errpos += 1
                nextchar = char2num(result[errpos])
                if( (nextchar == 64) || (errpos > strlen(result)) ) // "@" = 64 marks the end
                    break
                endif
                // replace 0 or . from front with @ until something else is encountered
                if( (nextchar == 46) || (nextchar == 48) )
                    result[errpos, errpos] = "@"
                else
                    break
                endif
            while( 1 )
            result = ReplaceString("@", result, "") // zap all "@"
            result = ReplaceString("()", result, "")    // zap brackets if they are empty
        endif
        
// case 2: error is zero (abbreviated format)
    else    // remove all elements pertaining to error
        format = ReplaceString(" e", format, "")    // try removing "e" placeholder with leading space
        format = ReplaceString("e", format, "") // remove "e" place holder anyway
        format = ReplaceString(" ±", format, "")   // try removing "±" with leading space
        format = ReplaceString("±", format, "")    // remove "±" anyway
        format = ReplaceString("(", format, "") // remove brackets
        format = ReplaceString(")", format, "")
        format += "%s"
// print whole string
        sprintf result, format, value, pref
    endif
    return result
end