+ GNU AFFERO GENERAL PUBLIC LICENSE
+ Version 3, 19 November 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
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+ Preamble
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+ 14. Revised Versions of this License.
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+ 15. Disclaimer of Warranty.
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+ THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
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+ 17. Interpretation of Sections 15 and 16.
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+ If the disclaimer of warranty and limitation of liability provided
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+ END OF TERMS AND CONDITIONS
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+ How to Apply These Terms to Your New Programs
+
+ If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+ To do so, attach the following notices to the program. It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+ <one line to give the program's name and a brief idea of what it does.>
+ Copyright (C) <year> <name of author>
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU Affero General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU Affero General Public License for more details.
+
+ You should have received a copy of the GNU Affero General Public License
+ along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+ If your software can interact with users remotely through a computer
+network, you should also make sure that it provides a way for users to
+get its source. For example, if your program is a web application, its
+interface could display a "Source" link that leads users to an archive
+of the code. There are many ways you could offer source, and different
+solutions will be better for different programs; see section 13 for the
+specific requirements.
+
+ You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU AGPL, see
+<https://www.gnu.org/licenses/>.
+# Introduction
+
+**fstop-print-calc** calculates times relative to a base time
+using fractions of f-stops.
+
+# F-stop printing
+
+F-stop printing refers to the concept of working in fractions of
+an f-stop when enlarging photographic prints, rather than linear
+time.
+
+Instead of making a test strip of 5, 10, 15, 20, and 25 second
+increments, you might make a strip in +0, +1/3, +2/3, +1, and +4/3
+*stops* relative to a 5s base time.
+
+The primary advantages are that test strips are created in
+standardized units, and a print documented in terms of f-stops can
+be reproduced accurately with different lenses, aperatures, and
+sizes.
+
+
+# The calculator
+
+For the most basic usage, simply run the program with a base time
+and it will show +/- 3 stops in 1/3rd stop increments:
+
+`$ fstop-print-calc 16`
+
+Instead of calculating a range of values, you can calculate one
+specific value by specifying it in the format `+X/Y` or `-X/Y`.
+To see +5/3rds stop:
+
+`$ fstop-print-calc 16 -- +5/3`
+
+You can specify the number of stops to display in each direction
+with `--stops`. This will show from -5 to +5 stops from the base:
+
+`$ fstop-print-calc 16 --stops 5`
+
+You can specify the fraction of stops to use with `--fraction`.
+This will show +/- 3 stops in 1/4th stop steps:
+
+`$ fstop-print-calc 16 --fraction 4`
+
+You can specify `--fraction` several times, too. This shows 1/4,
+1/3, and 1/2 steps combined:
+
+`$ fstop-print-calc 16 --fraction 2 --fraction 3 --fraction 4`
+
+You can output the data in CSV format:
+
+`$ fstop-print-calc 16 --csv`
+
+Or you can output an entire CSV table, with each row being offset
+from the next and previous row by an f-stop fraction. Generate a
++/-3 stop table in 1/3rd stop increments (19x19 table), with:
+
+`$ fstop-print-calc 16 --stops 3 --csv --csv-stops 3 --csv-fraction 3`
+
+
+# The math
+
+Fractional stops work the same as a compounding growth equation,
+where multiplying the base time (b) by some growth factor (x)
+repeatedly (N) times doubles the base time (1 stop increase). So:
+
+```
+b*x^N = 2*b
+ => x^N = 2 [base cancels]
+ => x = Nth_root(2) [Nth root of both sides]
+ => x = 2^(1/N) [alternate equivalent form]
+```
+
+N is the fraction of a stop, and calculating for x finds an
+exponential growth factor.
+
+An example for 1/3rd stop increments:
+
+* N is 3 (denominator of 1/3)
+* growth factor x calculated as x = 2^(1/3) = 1.25992
+* base b chosen to be 10 seconds
+* b + 1/3rd stop = 10 * 1.25992^1 = 12.599s
+* b + 2/3rd stop = 10 * 1.25992^2 = 15.874s
+* b + 3/3rd stop = 10 * 1.25992^3 = 20.000s
+
+This works for any fraction, and for positive or negative exponents.
+
+
+# License (AGPL Version 3.0)
+
+fstop-print-calc - an f-stop enlarging time calculator
+Copyright (C) 2024 Trevor Bentley <fstop-print-calc@x.mrmekon.com>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU Affero General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU Affero General Public License for more details.
+
+You should have received a copy of the GNU Affero General Public License
+along with this program. If not, see <https://www.gnu.org/licenses/>.
+//! # Introduction
+//!
+//! **fstop-print-calc** calculates times relative to a base time
+//! using fractions of f-stops.
+//!
+//! # F-stop printing
+//!
+//! F-stop printing refers to the concept of working in fractions of
+//! an f-stop when enlarging photographic prints, rather than linear
+//! time.
+//!
+//! Instead of making a test strip of 5, 10, 15, 20, and 25 second
+//! increments, you might make a strip in +0, +1/3, +2/3, +1, and +4/3
+//! *stops* relative to a 5s base time.
+//!
+//! The primary advantages are that test strips are created in
+//! standardized units, and a print documented in terms of f-stops can
+//! be reproduced accurately with different lenses, aperatures, and
+//! sizes.
+//!
+//!
+//! # The calculator
+//!
+//! For the most basic usage, simply run the program with a base time
+//! and it will show +/- 3 stops in 1/3rd stop increments:
+//!
+//! `$ fstop-print-calc 16`
+//!
+//! Instead of calculating a range of values, you can calculate one
+//! specific value by specifying it in the format `+X/Y` or `-X/Y`.
+//! To see +5/3rds stop:
+//!
+//! `$ fstop-print-calc 16 -- +5/3`
+//!
+//! You can specify the number of stops to display in each direction
+//! with `--stops`. This will show from -5 to +5 stops from the base:
+//!
+//! `$ fstop-print-calc 16 --stops 5`
+//!
+//! You can specify the fraction of stops to use with `--fraction`.
+//! This will show +/- 3 stops in 1/4th stop steps:
+//!
+//! `$ fstop-print-calc 16 --fraction 4`
+//!
+//! You can specify `--fraction` several times, too. This shows 1/4,
+//! 1/3, and 1/2 steps combined:
+//!
+//! `$ fstop-print-calc 16 --fraction 2 --fraction 3 --fraction 4`
+//!
+//! You can output the data in CSV format:
+//!
+//! `$ fstop-print-calc 16 --csv`
+//!
+//! Or you can output an entire CSV table, with each row being offset
+//! from the next and previous row by an f-stop fraction. Generate a
+//! +/-3 stop table in 1/3rd stop increments (19x19 table), with:
+//!
+//! `$ fstop-print-calc 16 --stops 3 --csv --csv-stops 3 --csv-fraction 3`
+//!
+//!
+//! # The math
+//!
+//! Fractional stops work the same as a compounding growth equation,
+//! where multiplying the base time (b) by some growth factor (x)
+//! repeatedly (N) times doubles the base time (1 stop increase). So:
+//!
+//! ```
+//! b*x^N = 2*b
+//! => x^N = 2 [base cancels]
+//! => x = Nth_root(2) [Nth root of both sides]
+//! => x = 2^(1/N) [alternate equivalent form]
+//! ```
+//!
+//! N is the fraction of a stop, and calculating for x finds an
+//! exponential growth factor.
+//!
+//! An example for 1/3rd stop increments:
+//!
+//! * N is 3 (denominator of 1/3)
+//! * growth factor x calculated as x = 2^(1/3) = 1.25992
+//! * base b chosen to be 10 seconds
+//! * b + 1/3rd stop = 10 * 1.25992^1 = 12.599s
+//! * b + 2/3rd stop = 10 * 1.25992^2 = 15.874s
+//! * b + 3/3rd stop = 10 * 1.25992^3 = 20.000s
+//!
+//! This works for any fraction, and for positive or negative exponents.
+//!
+//!
+// # License (AGPL Version 3.0)
+//
+// fstop-print-calc - an f-stop enlarging time calculator
+// Copyright (C) 2024 Trevor Bentley <fstop-print-calc@x.mrmekon.com>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+//
+use clap::Parser;
+use clap_num::number_range;
+
+const MAX_DENOMINATOR: usize = 16;
+
+fn frac_range(s: &str) -> Result<usize, String> {
+ number_range(s, 1, MAX_DENOMINATOR)
+}
+
+/// fstop-print-calc calculates exposure times relative to a base time
+/// using fractions of f-stops.
+#[derive(Parser, Debug)]
+struct CalcArgs {
+ /// Starting time to calculate relative to.
+ time: f64,
+
+ /// Specific fractional stop to calculate instead of producing tables, ex: +7/3
+ stop: Option<String>,
+
+ /// Stop fraction to calculate (1-16). Can be provided multiple times (default: 3 i.e. 1/3rd stop)
+ #[arg(short, long, value_parser=frac_range)]
+ fraction: Vec<usize>,
+
+ /// Number of whole stops to calculate in each direction (default: 3)
+ #[arg(short, long)]
+ stops: Option<i32>,
+
+ /// Round to this many decimal digits (default: 1)
+ #[arg(short, long)]
+ precision: Option<usize>,
+
+ /// Output in CSV format. Single row by default, or table if csv-fraction and csv-stops specified.
+ #[arg(short, long)]
+ csv: bool,
+
+ /// Stop fraction to use for CSV table. Only one permitted (default: 3 i.e. 1/3rd stop)
+ #[arg(long)]
+ csv_fraction: Option<usize>,
+
+ /// Number of whole stops to output in CSV table.
+ #[arg(long)]
+ csv_stops: Option<usize>,
+}
+
+fn fstop_calc(base: f64, num: f64, denom: f64, sign: f64) -> f64 {
+ // This is a compounding growth equation, where multiplying the
+ // base time (b) by some growth factor (x) repeatedly (N) times
+ // doubles the base time (1 stop increase). So:
+ //
+ // b*x^N = 2*b
+ // => x^N = 2 [base cancels]
+ // => x = Nth_root(2) [Nth root of both sides]
+ // => x = 2^(1/N) [alternate equivalent form]
+ //
+ // N is the fraction of a stop, and calculating for x finds an
+ // exponential growth factor.
+ let growth: f64 = (2_f64).powf(1./denom as f64);
+
+ let multiplier: f64 = (sign as i64 * num as i64 / denom as i64) as f64;
+ let modulo: f64 = (num % denom) as f64;
+ base*growth.powf(multiplier*denom + sign * modulo)
+}
+
+fn fstop_offset_str(num: f64, denom: f64, sign: f64, indent: usize, modulo: bool) -> String {
+ let sign_str = match sign {
+ -1.0 => "-",
+ _ => "+",
+ };
+ if denom == 1.0 {
+ let mult: f64 = (sign as i64 * num as i64 / denom as i64) as f64;
+ format!("{}{}", sign_str, mult.abs())
+ }
+ else {
+ let num = match modulo {
+ false => num,
+ true => (num % denom) as f64,
+ };
+ format!("{}{}{}/{}", " ".repeat(indent), sign_str, num, denom)
+ }
+}
+
+fn fstop_strings(base: f64, num: f64, denom: f64, sign: f64, indent: usize, p: usize, modulo: bool) -> (String, String) {
+ let off_str = fstop_offset_str(num, denom, sign, indent, modulo);
+ let val = fstop_calc(base, num, denom, sign);
+ (off_str, format!("{:.p$}", val, p=p))
+}
+
+fn fstop_print(base: f64, num: f64, denom: f64, sign: f64, indent: usize, p: usize, modulo: bool) {
+ let (offs, val) = fstop_strings(base, num, denom, sign, indent, p, modulo);
+ println!("{}: {}", offs, val);
+}
+
+fn print_csv_header(base: f64, stops: i32, fractions: &Vec<(u32, u32)>, p: usize) {
+ // offset header (negative)
+ for i in (0..stops).rev() {
+ let (i, sign) = (-i as f64, -1.0);
+ for (num, denom) in fractions.iter().rev() {
+ let num = *num as f64 + (-i as f64 * *denom as f64);
+ let (offs, _val) = fstop_strings(base, num, *denom as f64, sign, 0, p, true);
+ print!("'{offs}',");
+ }
+ }
+
+ // offset header (base)
+ let (offs, _val) = fstop_strings(base, 0.0, 1.0, 1.0, 0, p, true);
+ print!("'{offs}',");
+
+ // offset header (positive)
+ for i in 0..stops {
+ let (i, sign) = (i as f64, 1.0);
+ for (num, denom) in fractions {
+ let num = *num as f64 + (i as f64 * *denom as f64);
+ let (offs, _val) = fstop_strings(base, num, *denom as f64, sign, 0, p, true);
+ print!("'{offs}',");
+ }
+ }
+ println!();
+}
+
+fn print_csv_row(base: f64, stops: i32, fractions: &Vec<(u32, u32)>, p: usize) {
+ // values (negative)
+ for i in (0..stops).rev() {
+ let (i, sign) = (-i as f64, -1.0);
+ for (num, denom) in fractions.iter().rev() {
+ let num = *num as f64 + (-i as f64 * *denom as f64);
+ let (_offs, val) = fstop_strings(base, num, *denom as f64, sign, 0, p, true);
+ print!("{val},");
+ }
+ }
+
+ // values (base)
+ let (_offs, val) = fstop_strings(base, 0.0, 1.0, 1.0, 0, p, true);
+ print!("{val},");
+
+ // values (positive)
+ for i in 0..stops {
+ let (i, sign) = (i as f64, 1.0);
+ for (num, denom) in fractions {
+ let num = *num as f64 + (i as f64 * *denom as f64);
+ let (_offs, val) = fstop_strings(base, num, *denom as f64, sign, 0, p, true);
+ print!("{val},");
+ }
+ }
+ println!();
+}
+
+fn print_csv_table(base: f64, stops: i32, fractions: &Vec<(u32, u32)>, csv_stops: &Option<usize>, csv_fraction: &Option<usize>, p: usize) {
+ // If both stops and fraction specified, output a full table
+ match (csv_stops, csv_fraction) {
+ (Some(csv_stops), Some(csv_fraction)) => {
+ let csv_stops = *csv_stops as i32;
+ let csv_fraction = *csv_fraction as u32;
+ let mut csv_fractions: Vec<(u32, u32)> = vec!();
+ for num in 1..csv_fraction {
+ csv_fractions.push((num as u32, csv_fraction));
+ }
+ csv_fractions.push((1, 1));
+
+ print_csv_header(base, csv_stops, &csv_fractions, p);
+
+ // calculate and print all of the negative and +0 rows
+ let tmp_base = fstop_calc(base, -stops as f64 * csv_fraction as f64, csv_fraction as f64, 1.0);
+ print_csv_row(tmp_base, csv_stops, &csv_fractions, p);
+ for i in (0..stops).rev() {
+ for j in (0..csv_fraction).rev() {
+ let num = (i as f64 * csv_fraction as f64) + j as f64;
+ let tmp_base = fstop_calc(base, num, csv_fraction as f64, -1.0);
+ print_csv_row(tmp_base, csv_stops, &csv_fractions, p);
+ }
+ }
+
+ // calculate and print all of the positive rows
+ for i in 0..stops {
+ for j in 0..csv_fraction {
+ if i == 0 && j == 0 {
+ continue; // don't duplicate base
+ }
+ let num = (i as f64 * csv_fraction as f64) + j as f64;
+ let tmp_base = fstop_calc(base, num, csv_fraction as f64, 1.0);
+ print_csv_row(tmp_base, csv_stops, &csv_fractions, p);
+ }
+ }
+ let tmp_base = fstop_calc(base, stops as f64 * csv_fraction as f64, csv_fraction as f64, 1.0);
+ print_csv_row(tmp_base, csv_stops, &csv_fractions, p);
+ },
+ _ => {
+ // output a single row
+ print_csv_header(base, stops, fractions, p);
+ print_csv_row(base, stops, fractions, p);
+ },
+ }
+}
+
+fn main() {
+ let cli: CalcArgs = CalcArgs::parse();
+
+ // options specified at command line
+ let base = cli.time;
+ let stops = cli.stops.unwrap_or(3);
+ let p = cli.precision.unwrap_or(1);
+
+ // default to 1/3rd of a stop
+ let enabled_fracs = match cli.fraction.len() {
+ 0 => vec!(3),
+ _ => cli.fraction,
+ };
+
+ if let Some(stop) = cli.stop {
+ // parse string manually:
+ let (sign_str, fraction) = stop.split_at(1);
+ let sign: f64 = match sign_str {
+ "+" => { 1. },
+ "-" => { -1. },
+ _ => panic!("Stop missing +/- sign. Format must be +X/Y or -X/Y."),
+ };
+ let slash_offs = fraction.find("/").expect("Stop missing fractional slash. Format must be +X/Y or -X/Y.");
+ let (num, denom) = fraction.split_at(slash_offs);
+ let denom: &str = &denom[1..];
+ let _ = frac_range(denom).expect(&format!("Stop denominator not in range 1-{}. Format must be +X/Y or -X/Y.", MAX_DENOMINATOR));
+ let num: f64 = num.parse::<u32>().expect("Stop numerator not an integer. Format must be +X/Y or -X/Y.") as f64;
+ let denom: f64 = denom.parse::<u32>().expect("Stop numerator not an integer. Format must be +X/Y or -X/Y.") as f64;
+
+ // calculate and print result
+ fstop_print(base, num, denom, sign, 0, p, false);
+ return;
+ }
+
+ // build a list of all possible fractions
+ let mut fractions: Vec<(u32, u32)> = vec!();
+ for denom in &enabled_fracs {
+ for num in 1..*denom {
+ fractions.push((num as u32, *denom as u32));
+ }
+ }
+
+ // sort fractions
+ fractions.sort_by(|a, b| {
+ let fa: f64 = a.0 as f64 / a.1 as f64;
+ let fb: f64 = b.0 as f64 / b.1 as f64;
+ fa.partial_cmp(&fb).expect("Could not compare fractions.")
+ });
+
+ // remove duplicates (ex: 1/2 == 2/4 == 3/6)
+ fractions.dedup_by(|a, b| {
+ let fa: f64 = a.0 as f64 / a.1 as f64;
+ let fb: f64 = b.0 as f64 / b.1 as f64;
+ fa == fb
+ });
+
+ // always include 1/1
+ fractions.push((1, 1));
+
+
+ if cli.csv {
+ print_csv_table(base, stops, &fractions, &cli.csv_stops, &cli.csv_fraction, p);
+ }
+ else {
+ // calculate & print negative values
+ for i in (0..stops).rev() {
+ let (i, sign) = (-i as f64, -1.0);
+ for (num, denom) in fractions.iter().rev() {
+ let num = *num as f64 + (-i as f64 * *denom as f64);
+ fstop_print(base, num, *denom as f64, sign, 2, p, true);
+ }
+ }
+
+ // base
+ println!("+0: {:.p$}", base as f64, p=p);
+
+ // calculate & print positive values
+ for i in 0..stops {
+ let (i, sign) = (i as f64, 1.0);
+ for (num, denom) in &fractions {
+ let num = *num as f64 + (i as f64 * *denom as f64);
+ fstop_print(base, num, *denom as f64, sign, 2, p, true);
+ }
+ }
+ }
+}