Add test basic 'a' function

base.h

@@ -11,6 +11,8 @@
 typedef char Term;
 typedef uint32_t U32;
 typedef int32_t I32;
+typedef uint64_t U64;
+typedef int64_t I64;
 
 typedef struct {
   Term* buffer;

field.c

@@ -111,6 +111,16 @@ Term field_peek(Field* f, U32 y, U32 x) {
   return f->buffer[y * f_width + x];
 }
 
+Term field_peek_relative(Field* f, U32 y, U32 x, I32 offs_y, I32 offs_x) {
+  I64 f_height = f->height;
+  I64 f_width = f->width;
+  I64 y0 = (I64)y + (I64)offs_y;
+  I64 x0 = (I64)x + (I64)offs_x;
+  if (y0 >= f_height || x0 >= f_width || y0 < 0 || x0 < 0)
+    return '.';
+  return f->buffer[y0 * f_width + x0];
+}
+
 void field_poke(Field* f, U32 y, U32 x, Term term) {
   size_t f_height = f->height;
   size_t f_width = f->width;
@@ -120,6 +130,17 @@ void field_poke(Field* f, U32 y, U32 x, Term term) {
   f->buffer[y * f_width + x] = term;
 }
 
+void field_poke_relative(Field* f, U32 y, U32 x, I32 offs_y, I32 offs_x,
+                         Term term) {
+  I64 f_height = f->height;
+  I64 f_width = f->width;
+  I64 y0 = (I64)y + (I64)offs_y;
+  I64 x0 = (I64)x + (I64)offs_x;
+  if (y0 >= f_height || x0 >= f_width || y0 < 0 || x0 < 0)
+    return;
+  f->buffer[y0 * f_width + x0] = term;
+}
+
 inline bool term_char_is_valid(char c) {
   return c >= '#' && c <= '~';
 }

field.h

@@ -10,7 +10,9 @@ void field_copy_subrect(Field* src, Field* dest, U32 src_y, U32 src_x,
 void field_fill_subrect(Field* f, U32 y, U32 x, U32 height, U32 width,
                         Term fill_char);
 Term field_peek(Field* f, U32 y, U32 x);
+Term field_peek_relative(Field* f, U32 y, U32 x, I32 offs_y, I32 offs_x);
 void field_poke(Field* f, U32 y, U32 x, Term term);
+void field_poke_relative(Field* f, U32 y, U32 x, I32 offs_y, I32 offs_x, Term term);
 
 void field_fput(Field* f, FILE* stream);
 

sim.c

@@ -1,6 +1,56 @@
 #include "field.h"
 #include "sim.h"
 
+static Term const indexed_terms[] = {
+    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd',
+    'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
+    's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '.', '*', ':', ';', '#',
+};
+
+enum { Terms_array_num = sizeof indexed_terms };
+
+static inline size_t index_of_term(Term c) {
+  for (size_t i = 0; i < Terms_array_num; ++i) {
+    if (indexed_terms[i] == c)
+      return i;
+  }
+  return SIZE_MAX;
+}
+
+static inline Term term_lowered(Term c) {
+  return (c >= 'A' && c <= 'Z') ? c - ('a' - 'A') : c;
+}
+
+static inline Term terms_sum(Term a, Term b) {
+  size_t ia = index_of_term(term_lowered(a));
+  size_t ib = index_of_term(term_lowered(b));
+  if (ia == SIZE_MAX) ia = 0;
+  if (ib == SIZE_MAX) ib = 0;
+  return indexed_terms[(ia + ib) % Terms_array_num];
+}
+
+static inline void act_a(Field* f, U32 y, U32 x) {
+  Term inp0 = field_peek_relative(f, y, x, 0, 1);
+  Term inp1 = field_peek_relative(f, y, x, 0, 2);
+  if (inp0 != '.' && inp1 != '.') {
+    Term t = terms_sum(inp0, inp1);
+    field_poke_relative(f, y, x, 1, 0, t);
+  }
+}
+
 void orca_run(Field* f) {
-  (void)f;
+  size_t ny = f->height;
+  size_t nx = f->width;
+  Term* f_buffer = f->buffer;
+  for (size_t iy = 0; iy < ny; ++iy) {
+    Term* row = f_buffer + iy * nx;
+    for (size_t ix = 0; ix < nx; ++ix) {
+      Term c = row[ix];
+      switch (c) {
+        case 'a':
+          act_a(f, iy, ix);
+          break;
+      }
+    }
+  }
 }