Start of expr, by Daniel Verkamp.

1 files changed, 272 insertions, 0 deletions

diff --git a/toys/pending/expr.c b/toys/pending/expr.c
new file mode 100644
index 00000000..949bb664
--- /dev/null
+++ b/toys/pending/expr.c
@@ -0,0 +1,272 @@
+/* expr.c - evaluate expression
+ *
+ * Copyright 2013 Daniel Verkamp <daniel@drv.nu>
+ *
+ * http://pubs.opengroup.org/onlinepubs/9699919799/utilities/expr.html
+
+USE_EXPR(NEWTOY(expr, NULL, TOYFLAG_USR|TOYFLAG_BIN))
+
+config EXPR
+  bool "expr"
+  default n
+  help
+    usage: expr args
+
+    Evaluate expression and print result.
+
+    The supported operators, in order of increasing precedence, are:
+
+    | & = > >= < <= != + - * / %
+
+    In addition, parentheses () are supported for grouping.
+*/
+
+// TODO: int overflow checking
+
+#define FOR_expr
+#include "toys.h"
+
+
+GLOBALS(
+  int argidx;
+)
+
+// Scalar value.
+// If s is NULL, the value is an integer (i).
+// If s is not NULL, the value is a string (s).
+struct value {
+  char *s;
+  long i;
+};
+
+static void parse_expr(struct value *ret, struct value *v);
+
+static void get_value(struct value *v)
+{
+  char *endp, *arg;
+
+  if (TT.argidx == toys.optc) {
+    v->i = 0;
+    v->s = ""; // signal end of expression
+    return;
+  }
+
+  if (TT.argidx >= toys.optc) {
+    error_exit("syntax error");
+  }
+
+  arg = toys.optargs[TT.argidx++];
+
+  v->i = strtol(arg, &endp, 10);
+  v->s = *endp ? arg : NULL;
+}
+
+
+// check if v matches a token, and consume it if so
+static int match(struct value *v, const char *tok)
+{
+  if (v->s && !strcmp(v->s, tok)) {
+    get_value(v);
+    return 1;
+  }
+
+  return 0;
+}
+
+// check if v is the integer 0 or the empty string
+static int is_zero(const struct value *v)
+{
+  return ((v->s && *v->s == '\0') || v->i == 0);
+}
+
+static char *num_to_str(long num)
+{
+  static char num_buf[21];
+  snprintf(num_buf, sizeof(num_buf), "%ld", num);
+  return num_buf;
+}
+
+static int cmp(const struct value *lhs, const struct value *rhs)
+{
+  if (lhs->s || rhs->s) {
+    // at least one operand is a string
+    char *ls = lhs->s ? lhs->s : num_to_str(lhs->i);
+    char *rs = rhs->s ? rhs->s : num_to_str(rhs->i);
+    return strcmp(ls, rs);
+  } else {
+    return lhs->i - rhs->i;
+  }
+}
+
+
+// operators
+
+struct op {
+  const char *tok;
+
+  // calculate "lhs op rhs" (e.g. lhs + rhs) and store result in lhs
+  void (*calc)(struct value *lhs, const struct value *rhs);
+};
+
+
+static void re(struct value *lhs, const struct value *rhs)
+{
+  error_exit("regular expression match not implemented");
+}
+
+static void mod(struct value *lhs, const struct value *rhs)
+{
+  if (lhs->s || rhs->s) error_exit("non-integer argument");
+  if (is_zero(rhs)) error_exit("division by zero");
+  lhs->i %= rhs->i;
+}
+
+static void divi(struct value *lhs, const struct value *rhs)
+{
+  if (lhs->s || rhs->s) error_exit("non-integer argument");
+  if (is_zero(rhs)) error_exit("division by zero");
+  lhs->i /= rhs->i;
+}
+
+static void mul(struct value *lhs, const struct value *rhs)
+{
+  if (lhs->s || rhs->s) error_exit("non-integer argument");
+  lhs->i *= rhs->i;
+}
+
+static void sub(struct value *lhs, const struct value *rhs)
+{
+  if (lhs->s || rhs->s) error_exit("non-integer argument");
+  lhs->i -= rhs->i;
+}
+
+static void add(struct value *lhs, const struct value *rhs)
+{
+  if (lhs->s || rhs->s) error_exit("non-integer argument");
+  lhs->i += rhs->i;
+}
+
+static void ne(struct value *lhs, const struct value *rhs)
+{
+  lhs->i = cmp(lhs, rhs) != 0;
+  lhs->s = NULL;
+}
+
+static void lte(struct value *lhs, const struct value *rhs)
+{
+  lhs->i = cmp(lhs, rhs) <= 0;
+  lhs->s = NULL;
+}
+
+static void lt(struct value *lhs, const struct value *rhs)
+{
+  lhs->i = cmp(lhs, rhs) < 0;
+  lhs->s = NULL;
+}
+
+static void gte(struct value *lhs, const struct value *rhs)
+{
+  lhs->i = cmp(lhs, rhs) >= 0;
+  lhs->s = NULL;
+}
+
+static void gt(struct value *lhs, const struct value *rhs)
+{
+  lhs->i = cmp(lhs, rhs) > 0;
+  lhs->s = NULL;
+}
+
+static void eq(struct value *lhs, const struct value *rhs)
+{
+  lhs->i = cmp(lhs, rhs) == 0;
+  lhs->s = NULL;
+}
+
+static void and(struct value *lhs, const struct value *rhs)
+{
+  if (is_zero(lhs) || is_zero(rhs)) {
+    lhs->i = 0;
+    lhs->s = NULL;
+  }
+}
+
+static void or(struct value *lhs, const struct value *rhs)
+{
+  if (is_zero(lhs)) {
+    *lhs = *rhs;
+  }
+}
+
+
+// operators in order of increasing precedence
+static const struct op ops[] = {
+  {"|",   or  },
+  {"&",   and },
+  {"=",   eq  },
+  {">",   gt  },
+  {">=",  gte },
+  {"<",   lt  },
+  {"<=",  lte },
+  {"!=",  ne  },
+  {"+",   add },
+  {"-",   sub },
+  {"*",   mul },
+  {"/",   divi},
+  {"%",   mod },
+  {":",   re  },
+  {"(",   NULL}, // special case - must be last
+};
+
+
+static void parse_parens(struct value *ret, struct value *v)
+{
+  if (match(v, "(")) {
+    parse_expr(ret, v);
+    if (!match(v, ")")) error_exit("syntax error"); // missing closing paren
+  } else {
+    // v is a string or integer - return it and get the next token
+    *ret = *v;
+    get_value(v);
+  }
+}
+
+static void parse_op(struct value *lhs, struct value *tok, const struct op *op)
+{
+  // special case parsing for parentheses
+  if (*op->tok == '(') {
+    parse_parens(lhs, tok);
+    return;
+  }
+
+  parse_op(lhs, tok, op + 1);
+  while (match(tok, op->tok)) {
+    struct value rhs;
+    parse_op(&rhs, tok, op + 1);
+    if (rhs.s && !*rhs.s) error_exit("syntax error"); // premature end of expression
+    op->calc(lhs, &rhs);
+  }
+}
+
+static void parse_expr(struct value *ret, struct value *v)
+{
+  parse_op(ret, v, ops); // start at the top of the ops table
+}
+
+void expr_main(void)
+{
+  struct value tok, ret = {0};
+
+  toys.exitval = 2; // if exiting early, indicate invalid expression
+
+  TT.argidx = 0;
+
+  get_value(&tok); // warm up the parser with the initial value
+  parse_expr(&ret, &tok);
+
+  if (!tok.s || *tok.s) error_exit("syntax error"); // final token should be end of expression
+
+  if (ret.s) printf("%s\n", ret.s);
+  else printf("%ld\n", ret.i);
+
+  exit(is_zero(&ret));
+}