awk: improve comments and constants, no code changes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 27 insertions, 20 deletions

diff --git a/editors/awk.c b/editors/awk.c
index cf5173938..d4491d3e7 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -307,13 +307,13 @@ static void debug_parse_print_tc(uint32_t n)
                    | TC_LENGTH)
 #define TS_CONCAT_R (TS_OPERAND | TS_UOPPRE)
 
-#define OF_RES1     0x010000
-#define OF_RES2     0x020000
-#define OF_STR1     0x040000
-#define OF_STR2     0x080000
-#define OF_NUM1     0x100000
-#define OF_CHECKED  0x200000
-#define OF_REQUIRED 0x400000
+#define OF_RES1     0x010000    /* evaluate(left_node) */
+#define OF_RES2     0x020000    /* evaluate(right_node) */
+#define OF_STR1     0x040000    /* ...and use its string value */
+#define OF_STR2     0x080000    /* ...and use its string value */
+#define OF_NUM1     0x100000    /* ...and use its numeric value */
+#define OF_REQUIRED 0x200000    /* left_node must not be NULL */
+#define OF_CHECKED  0x400000    /* range pattern flip-flop bit */
 
 /* combined operator flags */
 #define xx      0
@@ -331,17 +331,18 @@ static void debug_parse_print_tc(uint32_t n)
 #define OPCLSMASK 0xFF00
 #define OPNMASK   0x007F
 
-/* operator priority is a highest byte (even: r->l, odd: l->r grouping)
- * (for builtins it has different meaning)
+/* operator precedence is the highest byte (even: r->l, odd: l->r grouping)
+ * (for builtins the byte has a different meaning)
  */
 #undef P
 #undef PRIMASK
 #undef PRIMASK2
+#define PRIMASK   0x7F000000
+#define PRIMASK2  0x7E000000
 /* Smaller 'x' means _higher_ operator precedence */
 #define PRECEDENCE(x) (x << 24)
 #define P(x)      PRECEDENCE(x)
-#define PRIMASK   0x7F000000
-#define PRIMASK2  0x7E000000
+#define LOWEST_PRECEDENCE PRIMASK
 
 /* Operation classes */
 #define SHIFT_TIL_THIS  0x0600
@@ -1424,7 +1425,7 @@ static node *parse_expr(uint32_t term_tc)
         debug_parse_print_tc(term_tc);
         debug_printf_parse("\n");
 
-        sn.info = PRIMASK;
+        sn.info = LOWEST_PRECEDENCE;
         sn.r.n = sn.a.n = getline_node = NULL;
         expected_tc = TS_OPERAND | TS_UOPPRE | TC_REGEXP | term_tc;
 
@@ -1443,7 +1444,7 @@ static node *parse_expr(uint32_t term_tc)
                 if (tc & (TS_BINOP | TC_UOPPOST)) {
                         debug_printf_parse("%s: TS_BINOP | TC_UOPPOST tc:%x\n", __func__, tc);
                         /* for binary and postfix-unary operators, jump back over
-                         * previous operators with higher priority */
+                         * previous operators with higher precedence */
                         vn = cn;
                         while (((t_info & PRIMASK) > (vn->a.n->info & PRIMASK2))
                             || (t_info == vn->info && t_info == TI_COLON)
@@ -1451,7 +1452,7 @@ static node *parse_expr(uint32_t term_tc)
                                 vn = vn->a.n;
                                 if (!vn->a.n) syntax_error(EMSG_UNEXP_TOKEN);
                         }
-                        if (t_info == TI_TERNARY) /* "?" operator */
+                        if (t_info == TI_TERNARY) /* "?" token */
 //TODO: why?
                                 t_info += PRECEDENCE(6);
                         cn = vn->a.n->r.n = new_node(t_info);
@@ -1483,11 +1484,10 @@ static node *parse_expr(uint32_t term_tc)
                                 }
 
                                 expected_tc = TS_OPERAND | TS_UOPPRE | TC_REGEXP;
-                                if (t_info == TI_PGETLINE) {
-                                        /* it's a pipe token "|" */
-                                        next_token(TC_GETLINE);
-                                        /* give maximum priority to this pipe */
-                                        cn->info &= ~PRIMASK;
+                                if (t_info == TI_PGETLINE) { /* "|" token */
+                                        next_token(TC_GETLINE); /* must be folowed by "getline" */
+                                        /* give maximum precedence to this pipe */
+                                        cn->info &= ~PRIMASK; /* sets PRECEDENCE(0) */
                                         expected_tc = TS_OPERAND | TS_UOPPRE | TS_BINOP | term_tc;
                                 }
                         } else {
@@ -1498,7 +1498,7 @@ static node *parse_expr(uint32_t term_tc)
                         vn->a.n = cn;
                         continue;
                 }
-                /* It wasn't a binary or unary_postfix operator */
+                /* It wasn't a binary or postfix-unary operator */
 
                 debug_printf_parse("%s: other, t_info:%x\n", __func__, t_info);
                 /* for operands and prefix-unary operators, attach them
@@ -1572,6 +1572,13 @@ static node *parse_expr(uint32_t term_tc)
                         break;
 
                 case TC_GETLINE:
+                        /* "getline" is a function, not a statement.
+                         * Works in gawk:
+                         *  r = ["SHELL CMD" | ] getline [VAR] [<"FILE"]
+                         *  if (getline <"FILE" < 0) print "Can't read FILE"
+                         *  while ("SHELL CMD" | getline > 0) ...
+                         * Returns: 1 successful read, 0 EOF, -1 error (sets ERRNO)
+                         */
                         debug_printf_parse("%s: TC_GETLINE\n", __func__);
                         getline_node = cn;
                         expected_tc = TS_OPERAND | TS_UOPPRE | TS_BINOP | term_tc;