Create a function library for the evaluator, bring back the ICCC voltage divider

tools/kicad/Cargo.toml

@@ -0,0 +1,2 @@
+[workspace]
+members = ["kicad_rs", "kicad_functions"]

tools/kicad/kicad_functions/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "kicad_functions"
+version = "0.1.0"
+authors = ["Dennis Marttinen <[email protected]>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+evalexpr = "6.1"
+resistor-calc = { git = "https://github.com/racklet/resistor-calc.git", branch = "fix-no-expr_builder-compile", default-features = false }

tools/kicad/kicad_functions/src/idx.rs

@@ -0,0 +1,23 @@
+use crate::util::err;
+use evalexpr::{EvalexprError, EvalexprResult, Value};
+
+/// `index` retrieves tuple values based on the given index.
+/// - Usage: idx(<tuple>, <i>)
+/// - Example: idx(("a", "b", "c"), 1) -> "b"
+/// - Output: i:th value in the tuple (zero-indexed)
+pub(crate) fn index(argument: &Value) -> EvalexprResult<Value> {
+    let args = argument.as_tuple()?;
+    if let [target, index] = &args[..] {
+        let index = index.as_int()?;
+        return target
+            .as_tuple()?
+            .get(index as usize)
+            .ok_or(EvalexprError::CustomMessage(format!(
+                "index out of bounds: {}",
+                index
+            )))
+            .map(|v| v.clone());
+    }
+
+    err(&format!("unsupported argument count: {}", args.len()))
+}

tools/kicad/kicad_functions/src/lib.rs

@@ -0,0 +1,14 @@
+mod idx;
+pub mod util;
+mod vdiv;
+
+use evalexpr::{EvalexprError, EvalexprResult, Value};
+
+// Match function for all custom functions available in the kicad_rs evaluator
+pub fn call_function(identifier: &str, argument: &Value) -> EvalexprResult<Value> {
+    match identifier {
+        "idx" => idx::index(argument),
+        "vdiv" => vdiv::voltage_divider(argument),
+        other => Err(EvalexprError::FunctionIdentifierNotFound(other.into())),
+    }
+}

tools/kicad/kicad_functions/src/util.rs

@@ -0,0 +1,6 @@
+use evalexpr::{EvalexprError, EvalexprResult};
+
+/// Returns an `EvalexprResult` with a `EvalexprError::CustomMessage` error
+pub fn err<T>(msg: &str) -> EvalexprResult<T> {
+    Err(EvalexprError::CustomMessage(msg.into()))
+}

tools/kicad/kicad_functions/src/vdiv.rs

@@ -0,0 +1,137 @@
+use crate::util::err;
+use evalexpr::{
+    ContextWithMutableVariables, EvalexprError, EvalexprResult, HashMapContext, Node, Value,
+};
+use resistor_calc::{RCalc, RRes, RSeries};
+use std::collections::HashSet;
+use std::panic::panic_any;
+
+fn parse_series(str: &str) -> EvalexprResult<&'static RSeries> {
+    match str.trim() {
+        "E3" => Ok(&resistor_calc::E3),
+        "E6" => Ok(&resistor_calc::E6),
+        "E12" => Ok(&resistor_calc::E12),
+        "E24" => Ok(&resistor_calc::E24),
+        "E48" => Ok(&resistor_calc::E48),
+        "E96" => Ok(&resistor_calc::E96),
+        _ => err(&format!("unknown resistor series: {}", str)),
+    }
+}
+
+// evalexpr is not smart enough to distinguish identifiers on its own
+fn unique_identifiers(e: &Node) -> usize {
+    let mut set = HashSet::new();
+    e.iter_variable_identifiers().for_each(|i| {
+        set.insert(i);
+    });
+    set.len()
+}
+
+struct VoltageDividerConfig {
+    target: f64,
+    expression: Node,
+    count: usize,
+    series: &'static RSeries,
+    resistance_min: Option<f64>,
+    resistance_max: Option<f64>,
+}
+
+impl VoltageDividerConfig {
+    fn parse(v: &Value) -> EvalexprResult<Self> {
+        let tuple = v.as_tuple()?;
+
+        let resistance_min = tuple.get(3).map(|v| v.as_number()).transpose()?;
+        let resistance_max = tuple.get(4).map(|v| v.as_number()).transpose()?;
+
+        // TODO: Support external constants
+        if let [target, expression, series] = &tuple[..3] {
+            let expression = evalexpr::build_operator_tree(&expression.as_string()?)?;
+            let count = unique_identifiers(&expression);
+
+            Ok(Self {
+                target: target.as_number()?,
+                expression,
+                count,
+                series: parse_series(&series.as_string()?)?,
+                resistance_min,
+                resistance_max,
+            })
+        } else {
+            err(&format!("unsupported argument count: {}", tuple.len()))
+        }
+    }
+}
+
+fn calculate(config: &VoltageDividerConfig) -> Option<RRes> {
+    let calc = RCalc::new(vec![config.series; config.count]);
+
+    calc.calc(|set| {
+        if let Some(true) = config.resistance_min.map(|r| set.sum() < r) {
+            return None; // Sum of resistance less than minimum
+        }
+
+        if let Some(true) = config.resistance_max.map(|r| set.sum() > r) {
+            return None; // Sum of resistance larger than maximum
+        }
+
+        // TODO: Storing this externally and using interior mutability
+        //  could be helpful to avoid reallocating on every invocation.
+        let mut context = HashMapContext::new();
+        for i in 1..=config.count {
+            context
+                .set_value(format!("R{}", i).into(), Value::Float(set.r(i)))
+                .unwrap();
+        }
+
+        match config.expression.eval_with_context(&context) {
+            Ok(v) => Some((config.target - v.as_number().unwrap()).abs()),
+            Err(e) => match &e {
+                EvalexprError::DivisionError { divisor: d, .. } => {
+                    if let Ok(n) = d.as_number() {
+                        if n == 0.0 {
+                            // This soft-catch may be a bit redundant. Based on some testing the
+                            // internal conversions in evalexpr cause zero values to deviate
+                            // slightly from zero, thus avoiding division by zero even if you
+                            // explicitly write a zero division into the voltage divider equation.
+                            return None;
+                        }
+                    }
+                    panic_any(e) // No graceful way to handle this from the closure
+                }
+                _ => panic_any(e),
+            },
+        }
+    })
+}
+
+/// `voltage_divider` computes values for resistor-based voltage dividers.
+/// - Usage: vdiv(<target voltage>, <divider expression>, <resistor series>, (min resistance), (max resistance))
+/// - Example: vdiv(5.1, "(R1+R2)/R2*0.8", "E96", 500e3, 700e3)
+/// - Output: (<closest voltage>, <R1 value>, <R2 value>, ...)
+/// There can be arbitrary many resistors in the divider, but they must be named "R1", "R2", etc.
+/// The computed optimal resistance values are also presented in this order. The minimal and maximal
+/// resistance limits are optional parameters, and only consider the sum of the resistances of all
+/// resistors defined in the expression.
+pub(crate) fn voltage_divider(argument: &Value) -> EvalexprResult<Value> {
+    let config = VoltageDividerConfig::parse(argument)?;
+    if let Some(res) = calculate(&config) {
+        // Take the first result, these are ordered by increasing error
+        if let Some((v, set)) = res.iter().next() {
+            let voltage = config.target + fixed_to_floating(*v);
+            let mut tuple = vec![Value::from(voltage)];
+            for i in 1..=config.count {
+                tuple.push(Value::from(set.r(i)));
+            }
+            return Ok(Value::from(tuple));
+        }
+    }
+
+    err(&format!("no solution found: {}", argument))
+}
+
+// resistor_calc outputs error quantities as "fixed point" numbers by multiplying
+// a float by 1e9, rounding the result and converting to u64. We need to undo
+// that procedure here.
+fn fixed_to_floating(value: u64) -> f64 {
+    (value as f64) / 1e9
+}

tools/kicad_rs/Cargo.toml → tools/kicad/kicad_rs/Cargo.toml

@@ -8,6 +8,7 @@ edition = "2018"
 
 [dependencies]
 evalexpr = "6.1"
+kicad_functions = { path = "../kicad_functions" }
 kicad_parse_gen = { git = "https://github.com/productize/kicad-parse-gen", branch = "kicad5" }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"

tools/kicad_rs/src/eval/index.rs → tools/kicad/kicad_rs/src/eval/index.rs

@@ -74,9 +74,8 @@ impl<'a> Context for SheetIndex<'a> {
             .flatten()
     }
 
-    fn call_function(&self, _identifier: &str, _argument: &Value) -> EvalexprResult<Value> {
-        // TODO: Fixed function set (voltage divider etc.)
-        unimplemented!("functions are currently unsupported");
+    fn call_function(&self, identifier: &str, argument: &Value) -> EvalexprResult<Value> {
+        kicad_functions::call_function(identifier, argument)
     }
 }
 

tools/kicad_rs/src/parser.rs → tools/kicad/kicad_rs/src/parser.rs

@@ -210,8 +210,10 @@ pub fn parse_components(kicad_sch: &SchematicFile) -> DynamicResult<Vec<Componen
                 },
                 // Get the main key value. It is ok if it's empty, too.
                 value: Value::parse(get_component_attr_mapped(&comp, main_key, &m).or_empty_str()),
-                // As this field corresponds to the main key expression attribute, we can get the expression directly
-                expression: f.value.clone(),
+                // As this field corresponds to the main key expression attribute, we can get the
+                // expression directly. The Eeschema file escapes the field though, so it needs to
+                // be unescaped here first.
+                expression: unescape(&f.value),
                 // Optionally, get the unit and a comment
                 unit: get_component_attr_mapped(&comp, &unit_key, &m),
                 comment: get_component_attr_mapped(&comp, &comment_key, &m),
@@ -360,3 +362,41 @@ impl<T: AsRef<str>> SplitCharN for Option<T> {
         }
     }
 }
+
+fn unescape(s: &str) -> String {
+    let mut res = String::new();
+    let mut prev = 0 as char;
+
+    let mut iter = s.chars().peekable();
+    while let Some(c) = iter.next() {
+        let mut next_prev = c;
+        match c {
+            '\\' => {
+                if prev == '\\' {
+                    res.push('\\');
+                    next_prev = 0 as char; // Remove duplicate backslashes
+                } else if iter.peek().map(|next| next != &'\\').unwrap_or(true) {
+                    res.push('"'); // A lone backslash is actually a missing double quote
+                }
+            }
+            c => res.push(c),
+        }
+        prev = next_prev;
+    }
+
+    res
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_unescape() {
+        assert_eq!(r#"\""#, unescape(r"\\\"));
+        assert_eq!(
+            r#"vdiv(5.1, "(R1+\R2\\)/R2*0.8", 'E96', 500e3, 700e3)"#,
+            unescape(r"vdiv(5.1, \(R1+\\R2\\\\)/R2*0.8\, 'E96', 500e3, 700e3)")
+        )
+    }
+}