fix: cast index values to double when used in expression position in C code generation

models/subscript/subscript.dat

@@ -185,3 +185,30 @@ v[A2]
 v[A3]
 0	0
 1	0
+w[X1,Y1]
+0	0
+1	0
+w[X1,Y2]
+0	-1
+1	-1
+w[X1,Y3]
+0	-2
+1	-2
+w[X2,Y1]
+0	1
+1	1
+w[X2,Y2]
+0	0
+1	0
+w[X2,Y3]
+0	-1
+1	-1
+w[X3,Y1]
+0	2
+1	2
+w[X3,Y2]
+0	1
+1	1
+w[X3,Y3]
+0	0
+1	0

models/subscript/subscript.mdl

@@ -59,6 +59,14 @@ v[DimA] = IF THEN ELSE (DimA = A2, 1, 0)
   ~:SUPPLEMENTARY
 	|
 
+DimX: (X1-X3) ~~|
+DimY: (Y1-Y3) ~~|
+w[DimX,DimY] = DimX - DimY
+	~
+	~	dimensions used in expression position (where expression result can go negative)
+  ~:SUPPLEMENTARY
+	|
+
 ********************************************************
 	.Control
 ********************************************************~

packages/compile/src/generate/gen-equation-c.spec.ts

@@ -291,7 +291,7 @@ describe('generateEquation (Vensim -> C)', () => {
     expect(genC(vars.get('_x'))).toEqual(['_x = 1.0;'])
     expect(genC(vars.get('_y'))).toEqual([
       'for (size_t i = 0; i < 2; i++) {',
-      '_y[i] = _IF_THEN_ELSE((i + 1) == _x, 1.0, 0.0);',
+      '_y[i] = _IF_THEN_ELSE((((double)i) + 1) == _x, 1.0, 0.0);',
       '}'
     ])
   })
@@ -304,7 +304,7 @@ describe('generateEquation (Vensim -> C)', () => {
     expect(vars.size).toBe(1)
     expect(genC(vars.get('_y'))).toEqual([
       'for (size_t i = 0; i < 2; i++) {',
-      '_y[i] = _IF_THEN_ELSE((i + 1) == 2, 1.0, 0.0);',
+      '_y[i] = _IF_THEN_ELSE((((double)i) + 1) == 2, 1.0, 0.0);',
       '}'
     ])
   })
@@ -650,7 +650,11 @@ describe('generateEquation (Vensim -> C)', () => {
       x[DimA] = DimB ~~|
     `)
     expect(vars.size).toBe(1)
-    expect(genC(vars.get('_x'))).toEqual(['for (size_t i = 0; i < 2; i++) {', '_x[i] = (__map_dimb_dima[i] + 1);', '}'])
+    expect(genC(vars.get('_x'))).toEqual([
+      'for (size_t i = 0; i < 2; i++) {',
+      '_x[i] = (((double)__map_dimb_dima[i]) + 1);',
+      '}'
+    ])
   })
 
   it('should work for 1D equation with one mapped dimension name used in subscript position (separated/non-apply-to-all)', () => {
@@ -680,7 +684,7 @@ describe('generateEquation (Vensim -> C)', () => {
     expect(genC(vars.get('_selected_a_index'), 'init-constants')).toEqual(['_selected_a_index = 1.0;'])
     expect(genC(vars.get('_x'))).toEqual([
       'for (size_t i = 0; i < 2; i++) {',
-      '_x[i] = _IF_THEN_ELSE((i + 1) == _selected_a_index, 1.0, 0.0);',
+      '_x[i] = _IF_THEN_ELSE((((double)i) + 1) == _selected_a_index, 1.0, 0.0);',
       '}'
     ])
   })
@@ -708,7 +712,7 @@ describe('generateEquation (Vensim -> C)', () => {
     expect(genC(vars.get('_x'))).toEqual([
       'for (size_t i = 0; i < 2; i++) {',
       'for (size_t j = 0; j < 2; j++) {',
-      '_x[i][j] = ((i + 1) * 10.0) + (j + 1);',
+      '_x[i][j] = ((((double)i) + 1) * 10.0) + (((double)j) + 1);',
       '}',
       '}'
     ])
@@ -738,7 +742,7 @@ describe('generateEquation (Vensim -> C)', () => {
     expect(genC(vars.get('_x'))).toEqual([
       'for (size_t i = 0; i < 2; i++) {',
       'for (size_t j = 0; j < 2; j++) {',
-      '_x[i][j] = ((i + 1) * 10.0) + (j + 1);',
+      '_x[i][j] = ((((double)i) + 1) * 10.0) + (((double)j) + 1);',
       '}',
       '}'
     ])
@@ -3224,7 +3228,7 @@ describe('generateEquation (Vensim -> C)', () => {
     expect(genC(vars.get('_x[_five]'), 'init-constants')).toEqual(['_x[4] = 5.0;'])
     expect(genC(vars.get('_y'))).toEqual([
       'for (size_t i = 0; i < 3; i++) {',
-      '_y[i] = _x[_dimx[(size_t)(2 + ((i + 1) - 1.0))]];',
+      '_y[i] = _x[_dimx[(size_t)(2 + ((((double)i) + 1) - 1.0))]];',
       '}'
     ])
   })

packages/compile/src/generate/gen-expr.js

@@ -67,7 +67,7 @@ export function generateExpr(expr, ctx) {
         // plus one (since Vensim indices are one-based).
         const dimId = expr.varId
         const indexCode = ctx.cVarIndex(dimId)
-        return `(${indexCode} + 1)`
+        return `(${indexExpr(indexCode, ctx)} + 1)`
       } else if (isIndex(expr.varId)) {
         // This is a reference to a subscript/index that is being used in expression position.
         // In place of the subscript, emit the numeric index value of the subscript plus one
@@ -1020,3 +1020,32 @@ function minFunc(ctx) {
       throw new Error(`Unhandled output format '${ctx.outFormat}'`)
   }
 }
+
+/**
+ * Return the C or JS code for a subscript or dimension (loop index variable) used in
+ * expression position.
+ *
+ * @param {string} indexValue The index number or code.
+ * @param {GenExprContext} ctx The context used when generating code for the expression.
+ * @return {string} The generated C/JS code.
+ */
+function indexExpr(indexValue, ctx) {
+  switch (ctx.outFormat) {
+    case 'c':
+      // In the C case, we need to cast to double since the index variable will be
+      // of type `size_t`, which is an unsigned type, but we want a signed type for
+      // the rare cases where math is involved that makes it go negative
+      if (isNaN(indexValue)) {
+        // This is a (non-numeric) loop index variable reference, so cast to double
+        return `((double)${indexValue})`
+      } else {
+        // This is a numeric index, no cast is necessary
+        return indexValue
+      }
+    case 'js':
+      // In the JS case, no cast is necessary
+      return indexValue
+    default:
+      throw new Error(`Unhandled output format '${ctx.outFormat}'`)
+  }
+}

packages/compile/src/model/read-equations.spec.ts

@@ -10174,6 +10174,10 @@ describe('readEquations', () => {
         refId: '_v',
         subscripts: ['_dima']
       }),
+      v('w[DimX,DimY]', 'DimX-DimY', {
+        refId: '_w',
+        subscripts: ['_dimx', '_dimy']
+      }),
       v('FINAL TIME', '1', {
         refId: '_final_time',
         varType: 'const'

packages/compile/src/model/read-subscripts.spec.ts

@@ -607,7 +607,9 @@ describe('readSubscriptRanges + resolveSubscriptRanges', () => {
       dim('DimB', ['B1', 'B2', 'B3'], undefined, undefined, [dimMapping('DimA')], {
         _dima: []
       }),
-      dim('DimC', ['C1', 'C2', 'C3', 'C4', 'C5'])
+      dim('DimC', ['C1', 'C2', 'C3', 'C4', 'C5']),
+      dim('DimX', ['X1', 'X2', 'X3']),
+      dim('DimY', ['Y1', 'Y2', 'Y3'])
     ])
 
     const resolvedSubs = readAndResolveSubscripts('subscript')
@@ -641,6 +643,8 @@ describe('readSubscriptRanges + resolveSubscriptRanges', () => {
         _dima: ['_b1', '_b2', '_b3']
       }),
       dim('DimC', ['C1', 'C2', 'C3', 'C4', 'C5']),
+      dim('DimX', ['X1', 'X2', 'X3']),
+      dim('DimY', ['Y1', 'Y2', 'Y3']),
       // { name: '_a1', value: 0, size: 1, family: '_dima', mappings: {} },
       sub('A1', 'DimA', 0),
       // { name: '_a2', value: 1, size: 1, family: '_dima', mappings: {} },
@@ -657,7 +661,13 @@ describe('readSubscriptRanges + resolveSubscriptRanges', () => {
       sub('C2', 'DimC', 1),
       sub('C3', 'DimC', 2),
       sub('C4', 'DimC', 3),
-      sub('C5', 'DimC', 4)
+      sub('C5', 'DimC', 4),
+      sub('X1', 'DimX', 0),
+      sub('X2', 'DimX', 1),
+      sub('X3', 'DimX', 2),
+      sub('Y1', 'DimY', 0),
+      sub('Y2', 'DimY', 1),
+      sub('Y3', 'DimY', 2)
     ])
   })
 })

packages/compile/src/model/read-variables.spec.ts

@@ -1933,6 +1933,9 @@ describe('readVariables', () => {
       v('v[DimA]', 'IF THEN ELSE(DimA=A2,1,0)', {
         subscripts: ['_dima']
       }),
+      v('w[DimX,DimY]', 'DimX-DimY', {
+        subscripts: ['_dimx', '_dimy']
+      }),
       v('FINAL TIME', '1'),
       v('INITIAL TIME', '0'),
       v('SAVEPER', 'TIME STEP'),