From bd14770b0c8594ce5b0ab9b0b1249b72fc781dd3 Mon Sep 17 00:00:00 2001
From: Denys Vlasenko <dvlasenk@redhat.com>
Date: Mon, 13 Sep 2010 11:11:40 +0200
Subject: shell/math.c: small code shrink; fixed incomprehensible comments
function old new delta
arith_apply 1334 1304 -30
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
---
shell/math.c | 225 ++++++++++++++++++++++++++++++-----------------------------
1 file changed, 113 insertions(+), 112 deletions(-)
diff --git a/shell/math.c b/shell/math.c
index c698a442b..a9fbc8910 100644
--- a/shell/math.c
+++ b/shell/math.c
@@ -52,17 +52,18 @@
* than a comparable parser written in yacc. The supported operators are
* listed in #defines below. Parens, order of operations, and error handling
* are supported. This code is thread safe. The exact expression format should
- * be that which POSIX specifies for shells. */
-
-/* The code uses a simple two-stack algorithm. See
+ * be that which POSIX specifies for shells.
+ *
+ * The code uses a simple two-stack algorithm. See
* http://www.onthenet.com.au/~grahamis/int2008/week02/lect02.html
* for a detailed explanation of the infix-to-postfix algorithm on which
* this is based (this code differs in that it applies operators immediately
* to the stack instead of adding them to a queue to end up with an
- * expression). */
-
-/* To use the routine, call it with an expression string and error return
- * pointer */
+ * expression).
+ *
+ * To use the routine, call it with an expression string and error return
+ * pointer
+ */
/*
* Aug 24, 2001 Manuel Novoa III
@@ -104,22 +105,21 @@
* (C) 2003 Vladimir Oleynik <dzo@simtreas.ru>
*
* - allow access to variable,
- * used recursive find value indirection (c=2*2; a="c"; $((a+=2)) produce 6)
- * - realize assign syntax (VAR=expr, +=, *= etc)
- * - realize exponentiation (** operator)
- * - realize comma separated - expr, expr
- * - realise ++expr --expr expr++ expr--
- * - realise expr ? expr : expr (but, second expr calculate always)
+ * use recursive value indirection: c="2*2"; a="c"; echo $((a+=2)) produce 6
+ * - implement assign syntax (VAR=expr, +=, *= etc)
+ * - implement exponentiation (** operator)
+ * - implement comma separated - expr, expr
+ * - implement ++expr --expr expr++ expr--
+ * - implement expr ? expr : expr (but second expr is always calculated)
* - allow hexadecimal and octal numbers
- * - was restored loses XOR operator
- * - remove one goto label, added three ;-)
- * - protect $((num num)) as true zero expr (Manuel`s error)
+ * - restore lost XOR operator
+ * - protect $((num num)) as true zero expr (Manuel's error)
* - always use special isspace(), see comment from bash ;-)
*/
#include "libbb.h"
#include "math.h"
-#define a_e_h_t arith_eval_hooks_t
+#define a_e_h_t arith_eval_hooks_t
#define lookupvar (math_hooks->lookupvar)
#define setvar (math_hooks->setvar )
//#define endofname (math_hooks->endofname)
@@ -130,103 +130,104 @@ typedef unsigned char operator;
* precedence, and 3 high bits are an ID unique across operators of that
* precedence. The ID portion is so that multiple operators can have the
* same precedence, ensuring that the leftmost one is evaluated first.
- * Consider * and /. */
-
-#define tok_decl(prec,id) (((id)<<5)|(prec))
-#define PREC(op) ((op) & 0x1F)
-
-#define TOK_LPAREN tok_decl(0,0)
+ * Consider * and /
+ */
+#define tok_decl(prec,id) (((id)<<5) | (prec))
+#define PREC(op) ((op) & 0x1F)
-#define TOK_COMMA tok_decl(1,0)
+#define TOK_LPAREN tok_decl(0,0)
-#define TOK_ASSIGN tok_decl(2,0)
-#define TOK_AND_ASSIGN tok_decl(2,1)
-#define TOK_OR_ASSIGN tok_decl(2,2)
-#define TOK_XOR_ASSIGN tok_decl(2,3)
-#define TOK_PLUS_ASSIGN tok_decl(2,4)
-#define TOK_MINUS_ASSIGN tok_decl(2,5)
-#define TOK_LSHIFT_ASSIGN tok_decl(2,6)
-#define TOK_RSHIFT_ASSIGN tok_decl(2,7)
+#define TOK_COMMA tok_decl(1,0)
-#define TOK_MUL_ASSIGN tok_decl(3,0)
-#define TOK_DIV_ASSIGN tok_decl(3,1)
-#define TOK_REM_ASSIGN tok_decl(3,2)
+/* All assignments are right associative and have the same precedence,
+ * but there are 11 of them, which doesn't fit into 3 bits for unique id.
+ * Abusing another precedence level:
+ */
+#define TOK_ASSIGN tok_decl(2,0)
+#define TOK_AND_ASSIGN tok_decl(2,1)
+#define TOK_OR_ASSIGN tok_decl(2,2)
+#define TOK_XOR_ASSIGN tok_decl(2,3)
+#define TOK_PLUS_ASSIGN tok_decl(2,4)
+#define TOK_MINUS_ASSIGN tok_decl(2,5)
+#define TOK_LSHIFT_ASSIGN tok_decl(2,6)
+#define TOK_RSHIFT_ASSIGN tok_decl(2,7)
-/* all assign is right associativity and precedence eq, but (7+3)<<5 > 256 */
-#define convert_prec_is_assign(prec) do { if (prec == 3) prec = 2; } while (0)
+#define TOK_MUL_ASSIGN tok_decl(3,0)
+#define TOK_DIV_ASSIGN tok_decl(3,1)
+#define TOK_REM_ASSIGN tok_decl(3,2)
-/* conditional is right associativity too */
-#define TOK_CONDITIONAL tok_decl(4,0)
-#define TOK_CONDITIONAL_SEP tok_decl(4,1)
+#define fix_assignment_prec(prec) do { if (prec == 3) prec = 2; } while (0)
-#define TOK_OR tok_decl(5,0)
+/* ternary conditional operator is right associative too */
+#define TOK_CONDITIONAL tok_decl(4,0)
+#define TOK_CONDITIONAL_SEP tok_decl(4,1)
-#define TOK_AND tok_decl(6,0)
+#define TOK_OR tok_decl(5,0)
-#define TOK_BOR tok_decl(7,0)
+#define TOK_AND tok_decl(6,0)
-#define TOK_BXOR tok_decl(8,0)
+#define TOK_BOR tok_decl(7,0)
-#define TOK_BAND tok_decl(9,0)
+#define TOK_BXOR tok_decl(8,0)
-#define TOK_EQ tok_decl(10,0)
-#define TOK_NE tok_decl(10,1)
+#define TOK_BAND tok_decl(9,0)
-#define TOK_LT tok_decl(11,0)
-#define TOK_GT tok_decl(11,1)
-#define TOK_GE tok_decl(11,2)
-#define TOK_LE tok_decl(11,3)
+#define TOK_EQ tok_decl(10,0)
+#define TOK_NE tok_decl(10,1)
-#define TOK_LSHIFT tok_decl(12,0)
-#define TOK_RSHIFT tok_decl(12,1)
+#define TOK_LT tok_decl(11,0)
+#define TOK_GT tok_decl(11,1)
+#define TOK_GE tok_decl(11,2)
+#define TOK_LE tok_decl(11,3)
-#define TOK_ADD tok_decl(13,0)
-#define TOK_SUB tok_decl(13,1)
+#define TOK_LSHIFT tok_decl(12,0)
+#define TOK_RSHIFT tok_decl(12,1)
-#define TOK_MUL tok_decl(14,0)
-#define TOK_DIV tok_decl(14,1)
-#define TOK_REM tok_decl(14,2)
+#define TOK_ADD tok_decl(13,0)
+#define TOK_SUB tok_decl(13,1)
-/* exponent is right associativity */
-#define TOK_EXPONENT tok_decl(15,1)
+#define TOK_MUL tok_decl(14,0)
+#define TOK_DIV tok_decl(14,1)
+#define TOK_REM tok_decl(14,2)
-/* For now unary operators. */
-#define UNARYPREC 16
-#define TOK_BNOT tok_decl(UNARYPREC,0)
-#define TOK_NOT tok_decl(UNARYPREC,1)
+/* exponent is right associative */
+#define TOK_EXPONENT tok_decl(15,1)
-#define TOK_UMINUS tok_decl(UNARYPREC+1,0)
-#define TOK_UPLUS tok_decl(UNARYPREC+1,1)
+/* unary operators */
+#define UNARYPREC 16
+#define TOK_BNOT tok_decl(UNARYPREC,0)
+#define TOK_NOT tok_decl(UNARYPREC,1)
-#define PREC_PRE (UNARYPREC+2)
+#define TOK_UMINUS tok_decl(UNARYPREC+1,0)
+#define TOK_UPLUS tok_decl(UNARYPREC+1,1)
-#define TOK_PRE_INC tok_decl(PREC_PRE, 0)
-#define TOK_PRE_DEC tok_decl(PREC_PRE, 1)
+#define PREC_PRE (UNARYPREC+2)
-#define PREC_POST (UNARYPREC+3)
+#define TOK_PRE_INC tok_decl(PREC_PRE, 0)
+#define TOK_PRE_DEC tok_decl(PREC_PRE, 1)
-#define TOK_POST_INC tok_decl(PREC_POST, 0)
-#define TOK_POST_DEC tok_decl(PREC_POST, 1)
+#define PREC_POST (UNARYPREC+3)
-#define SPEC_PREC (UNARYPREC+4)
+#define TOK_POST_INC tok_decl(PREC_POST, 0)
+#define TOK_POST_DEC tok_decl(PREC_POST, 1)
-#define TOK_NUM tok_decl(SPEC_PREC, 0)
-#define TOK_RPAREN tok_decl(SPEC_PREC, 1)
+#define SPEC_PREC (UNARYPREC+4)
-#define NUMPTR (*numstackptr)
+#define TOK_NUM tok_decl(SPEC_PREC, 0)
+#define TOK_RPAREN tok_decl(SPEC_PREC, 1)
static int
tok_have_assign(operator op)
{
operator prec = PREC(op);
- convert_prec_is_assign(prec);
+ fix_assignment_prec(prec);
return (prec == PREC(TOK_ASSIGN) ||
prec == PREC_PRE || prec == PREC_POST);
}
static int
-is_right_associativity(operator prec)
+is_right_associative(operator prec)
{
return (prec == PREC(TOK_ASSIGN) || prec == PREC(TOK_EXPONENT)
|| prec == PREC(TOK_CONDITIONAL));
@@ -255,25 +256,25 @@ arith_lookup_val(v_n_t *t, a_e_h_t *math_hooks)
if (p) {
int errcode;
-
- /* recursive try as expression */
chk_var_recursive_looped_t *cur;
chk_var_recursive_looped_t cur_save;
+ /* recursively try p as expression */
+
for (cur = prev_chk_var_recursive; cur; cur = cur->next) {
if (strcmp(cur->var, t->var) == 0) {
/* expression recursion loop detected */
return -5;
}
}
- /* save current lookuped var name */
+ /* save current var name */
cur = prev_chk_var_recursive;
cur_save.var = t->var;
cur_save.next = cur;
prev_chk_var_recursive = &cur_save;
- t->val = arith (p, &errcode, math_hooks);
- /* restore previous ptr after recursiving */
+ t->val = arith(p, &errcode, math_hooks);
+ /* restore previous ptr after recursion */
prev_chk_var_recursive = cur;
return errcode;
}
@@ -283,21 +284,24 @@ arith_lookup_val(v_n_t *t, a_e_h_t *math_hooks)
return 0;
}
-/* "applying" a token means performing it on the top elements on the integer
- * stack. For a unary operator it will only change the top element, but a
- * binary operator will pop two arguments and push a result */
+/* "Applying" a token means performing it on the top elements on the integer
+ * stack. For an unary operator it will only change the top element, but a
+ * binary operator will pop two arguments and push the result */
static NOINLINE int
arith_apply(operator op, v_n_t *numstack, v_n_t **numstackptr, a_e_h_t *math_hooks)
{
+#define NUMPTR (*numstackptr)
+
v_n_t *numptr_m1;
arith_t numptr_val, rez;
int ret_arith_lookup_val;
/* There is no operator that can work without arguments */
- if (NUMPTR == numstack) goto err;
+ if (NUMPTR == numstack)
+ goto err;
numptr_m1 = NUMPTR - 1;
- /* check operand is var with noninteger value */
+ /* Check operand is var with noninteger value */
ret_arith_lookup_val = arith_lookup_val(numptr_m1, math_hooks);
if (ret_arith_lookup_val)
return ret_arith_lookup_val;
@@ -388,16 +392,13 @@ arith_apply(operator op, v_n_t *numstack, v_n_t **numstackptr, a_e_h_t *math_hoo
rez = rez ?
numptr_val : numptr_m1->contidional_second_val;
} else if (op == TOK_EXPONENT) {
+ arith_t c;
if (numptr_val < 0)
return -3; /* exponent less than 0 */
- else {
- arith_t c = 1;
-
- if (numptr_val)
- while (numptr_val--)
- c *= rez;
- rez = c;
- }
+ c = 1;
+ while (--numptr_val >= 0)
+ c *= rez;
+ rez = c;
} else if (numptr_val==0) /* zero divisor check */
return -2;
else if (op == TOK_DIV || op == TOK_DIV_ASSIGN)
@@ -422,11 +423,12 @@ arith_apply(operator op, v_n_t *numstack, v_n_t **numstackptr, a_e_h_t *math_hoo
rez++;
}
numptr_m1->val = rez;
- /* protect geting var value, is number now */
+ /* erase var name, it is just a number now */
numptr_m1->var = NULL;
return 0;
err:
return -1;
+#undef NUMPTR
}
/* longest must be first */
@@ -473,7 +475,6 @@ static const char op_tokens[] ALIGN1 = {
'(', 0, TOK_LPAREN,
0
};
-/* ptr to ")" */
#define ptr_to_rparen (&op_tokens[sizeof(op_tokens)-7])
const char* FAST_FUNC
@@ -529,15 +530,15 @@ arith(const char *expr, int *perrcode, a_e_h_t *math_hooks)
* result on the integer stack */
if (expr != ptr_to_rparen + 1) {
- /* If we haven't done so already, */
- /* append a closing right paren */
+ /* If we haven't done so already,
+ * append a closing right paren
+ * and let the loop process it */
expr = ptr_to_rparen;
- /* and let the loop process it. */
continue;
}
- /* At this point, we're done with the expression. */
+ /* At this point, we're done with the expression */
if (numstackptr != numstack + 1) {
- /* ... but if there isn't, it's bad */
+ /* ...but if there isn't, it's bad */
goto err;
}
if (numstack->var) {
@@ -619,11 +620,11 @@ arith(const char *expr, int *perrcode, a_e_h_t *math_hooks)
/* We don't want an unary operator to cause recursive descent on the
* stack, because there can be many in a row and it could cause an
* operator to be evaluated before its argument is pushed onto the
- * integer stack. */
- /* But for binary operators, "apply" everything on the operator
+ * integer stack.
+ * But for binary operators, "apply" everything on the operator
* stack until we find an operator with a lesser priority than the
- * one we have just extracted. */
- /* Left paren is given the lowest priority so it will never be
+ * one we have just extracted.
+ * Left paren is given the lowest priority so it will never be
* "applied" in this way.
* if associativity is right and priority eq, applied also skip
*/
@@ -641,17 +642,17 @@ arith(const char *expr, int *perrcode, a_e_h_t *math_hooks)
* hit an open paren nor the bottom of the stack, pop
* tokens and apply them */
if (prev_op == TOK_LPAREN) {
- /* Any operator directly after a */
+ /* Any operator directly after a
+ * close paren should consider itself binary */
lasttok = TOK_NUM;
- /* close paren should consider itself binary */
goto next;
}
} else {
operator prev_prec = PREC(prev_op);
- convert_prec_is_assign(prec);
- convert_prec_is_assign(prev_prec);
+ fix_assignment_prec(prec);
+ fix_assignment_prec(prev_prec);
if (prev_prec < prec
- || (prev_prec == prec && is_right_associativity(prec))
+ || (prev_prec == prec && is_right_associative(prec))
) {
stackptr++;
break;
--
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