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-rw-r--r--libbb/arith.c396
1 files changed, 253 insertions, 143 deletions
diff --git a/libbb/arith.c b/libbb/arith.c
index 04c45ec3d..362f7bb2b 100644
--- a/libbb/arith.c
+++ b/libbb/arith.c
@@ -24,19 +24,88 @@
* as a replacement for yacc-based parsers. However, it may well be faster
* than a comparable parser writen in yacc. The supported operators are
* listed in #defines below. Parens, order of operations, and error handling
- * are supported. This code is threadsafe. */
+ * are supported. This code is threadsafe. The exact expression format should
+ * 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 explaination 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 */
-/* To use the routine, call it with an expression string. It returns an
- * integer result. You will also need to define an "error" function
- * that takes printf arguments and _does not return_, or modify the code
- * to use another error mechanism. */
+/*
+ * Aug 24, 2001 Manuel Novoa III
+ *
+ * Reduced the generated code size by about 30% (i386) and fixed several bugs.
+ *
+ * 1) In arith_apply():
+ * a) Cached values of *numptr and &(numptr[-1]).
+ * b) Removed redundant test for zero denominator.
+ *
+ * 2) In arith():
+ * a) Eliminated redundant code for processing operator tokens by moving
+ * to a table-based implementation. Also folded handling of parens
+ * into the table.
+ * b) Combined all 3 loops which called arith_apply to reduce generated
+ * code size at the cost of speed.
+ *
+ * 3) The following expressions were treated as valid by the original code:
+ * 1() , 0! , 1 ( *3 ) .
+ * These bugs have been fixed by internally enclosing the expression in
+ * parens and then checking that all binary ops and right parens are
+ * preceded by a valid expression (NUM_TOKEN).
+ *
+ * Note: It may be desireable to replace Aaron's test for whitespace with
+ * ctype's isspace() if it is used by another busybox applet or if additional
+ * whitespace chars should be considered. Look below the "#include"s for a
+ * precompiler test.
+ */
+
+/*
+ * Aug 26, 2001 Manuel Novoa III
+ *
+ * Return 0 for null expressions. Pointed out by vodz.
+ *
+ * Merge in Aaron's comments previously posted to the busybox list,
+ * modified slightly to take account of my changes to the code.
+ *
+ * TODO: May want to allow access to variables in the arith code.
+ * This would:
+ * 1) allow us to evaluate $A as 0 if A isn't set (although this
+ * would require changes to ash.c too).
+ * 2) allow us to write expressions as $(( A + 2 )).
+ * This could be done using a callback function passed to the
+ * arith() function of by requiring such a function with fixed
+ * name as an extern.
+ */
#include <stdlib.h>
#include <string.h>
+#include <ctype.h>
#include "libbb.h"
+/*
+ * Use "#if 1" below for Aaron's original test for whitespace.
+ * Use "#if 0" for ctype's isspace().
+ * */
+#if 1
+#undef isspace
+#define isspace(arithval) \
+ (arithval == ' ' || arithval == '\n' || arithval == '\t')
+#endif
+
typedef char operator;
+/* An operator's token id is a bit of a bitfield. The lower 5 bits are the
+ * precedence, and high 3 are an ID unique accross 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)
@@ -70,194 +139,235 @@ typedef char operator;
#define TOK_DIV tok_decl(10,1)
#define TOK_REM tok_decl(10,2)
+/* For now all unary operators have the same precedence, and that's used to
+ * identify them as unary operators */
#define UNARYPREC 14
#define TOK_BNOT tok_decl(UNARYPREC,0)
#define TOK_NOT tok_decl(UNARYPREC,1)
#define TOK_UMINUS tok_decl(UNARYPREC,2)
+#define TOK_UPLUS tok_decl(UNARYPREC,3)
#define TOK_NUM tok_decl(15,0)
+#define TOK_RPAREN tok_decl(15,1)
+#define TOK_ERROR tok_decl(15,2) /* just a place-holder really */
#define ARITH_APPLY(op) arith_apply(op, numstack, &numstackptr)
#define NUMPTR (*numstackptr)
+
+/* "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 */
static short arith_apply(operator op, long *numstack, long **numstackptr)
{
- if (NUMPTR == numstack) goto err;
+ long numptr_val;
+ long *NUMPTR_M1;
+
+ if (NUMPTR == numstack) goto err; /* There is no operator that can work
+ without arguments */
+ NUMPTR_M1 = NUMPTR - 1;
if (op == TOK_UMINUS)
- NUMPTR[-1] *= -1;
+ *NUMPTR_M1 *= -1;
else if (op == TOK_NOT)
- NUMPTR[-1] = !(NUMPTR[-1]);
+ *NUMPTR_M1 = !(*NUMPTR_M1);
else if (op == TOK_BNOT)
- NUMPTR[-1] = ~(NUMPTR[-1]);
-
+ *NUMPTR_M1 = ~(*NUMPTR_M1);
+ else if (op != TOK_UPLUS) {
/* Binary operators */
- else {
- if (NUMPTR-1 == numstack) goto err;
- --NUMPTR;
+ if (NUMPTR_M1 == numstack) goto err; /* ... and binary operators need two
+ arguments */
+ numptr_val = *--NUMPTR; /* ... and they pop one */
+ NUMPTR_M1 = NUMPTR - 1;
if (op == TOK_BOR)
- NUMPTR[-1] |= *NUMPTR;
+ *NUMPTR_M1 |= numptr_val;
else if (op == TOK_OR)
- NUMPTR[-1] = *NUMPTR || NUMPTR[-1];
+ *NUMPTR_M1 = numptr_val || *NUMPTR_M1;
else if (op == TOK_BAND)
- NUMPTR[-1] &= *NUMPTR;
+ *NUMPTR_M1 &= numptr_val;
else if (op == TOK_AND)
- NUMPTR[-1] = NUMPTR[-1] && *NUMPTR;
+ *NUMPTR_M1 = *NUMPTR_M1 && numptr_val;
else if (op == TOK_EQ)
- NUMPTR[-1] = (NUMPTR[-1] == *NUMPTR);
+ *NUMPTR_M1 = (*NUMPTR_M1 == numptr_val);
else if (op == TOK_NE)
- NUMPTR[-1] = (NUMPTR[-1] != *NUMPTR);
+ *NUMPTR_M1 = (*NUMPTR_M1 != numptr_val);
else if (op == TOK_GE)
- NUMPTR[-1] = (NUMPTR[-1] >= *NUMPTR);
+ *NUMPTR_M1 = (*NUMPTR_M1 >= numptr_val);
else if (op == TOK_RSHIFT)
- NUMPTR[-1] >>= *NUMPTR;
+ *NUMPTR_M1 >>= numptr_val;
else if (op == TOK_LSHIFT)
- NUMPTR[-1] <<= *NUMPTR;
+ *NUMPTR_M1 <<= numptr_val;
else if (op == TOK_GT)
- NUMPTR[-1] = (NUMPTR[-1] > *NUMPTR);
+ *NUMPTR_M1 = (*NUMPTR_M1 > numptr_val);
else if (op == TOK_LT)
- NUMPTR[-1] = (NUMPTR[-1] < *NUMPTR);
+ *NUMPTR_M1 = (*NUMPTR_M1 < numptr_val);
else if (op == TOK_LE)
- NUMPTR[-1] = (NUMPTR[-1] <= *NUMPTR);
+ *NUMPTR_M1 = (*NUMPTR_M1 <= numptr_val);
else if (op == TOK_MUL)
- NUMPTR[-1] *= *NUMPTR;
- else if (op == TOK_DIV) {
- if(*NUMPTR==0)
- return -2;
- NUMPTR[-1] /= *NUMPTR;
- }
- else if (op == TOK_REM) {
- if(*NUMPTR==0)
- return -2;
- NUMPTR[-1] %= *NUMPTR;
- }
+ *NUMPTR_M1 *= numptr_val;
else if (op == TOK_ADD)
- NUMPTR[-1] += *NUMPTR;
+ *NUMPTR_M1 += numptr_val;
else if (op == TOK_SUB)
- NUMPTR[-1] -= *NUMPTR;
+ *NUMPTR_M1 -= numptr_val;
+ else if(numptr_val==0) /* zero divisor check */
+ return -2;
+ else if (op == TOK_DIV)
+ *NUMPTR_M1 /= numptr_val;
+ else if (op == TOK_REM)
+ *NUMPTR_M1 %= numptr_val;
+ /* WARNING!!! WARNING!!! WARNING!!! */
+ /* Any new operators should be added BEFORE the zero divisor check! */
}
return 0;
err: return(-1);
}
-extern long arith (const char *startbuf, int *errcode)
-{
- register char arithval;
- const char *expr = startbuf;
+static const char endexpression[] = ")";
- operator lasttok = TOK_MUL, op;
- size_t datasizes = strlen(startbuf);
+/* + and - (in that order) must be last */
+static const char op_char[] = "!<>=|&*/%~()+-";
+static const char op_token[] = {
+ /* paired with equal */
+ TOK_NE, TOK_LE, TOK_GE,
+ /* paired with self -- note: ! is special-cased below*/
+ TOK_ERROR, TOK_LSHIFT, TOK_RSHIFT, TOK_EQ, TOK_OR, TOK_AND,
+ /* singles */
+ TOK_NOT, TOK_LT, TOK_GT, TOK_ERROR, TOK_BOR, TOK_BAND,
+ TOK_MUL, TOK_DIV, TOK_REM, TOK_BNOT, TOK_LPAREN, TOK_RPAREN,
+ TOK_ADD, TOK_SUB, TOK_UPLUS, TOK_UMINUS
+};
+
+#define NUM_PAIR_EQUAL 3
+#define NUM_PAIR_SAME 6
+
+extern long arith (const char *expr, int *errcode)
+{
+ register char arithval; /* Current character under analysis */
+ operator lasttok, op;
unsigned char prec;
- long *numstack, *numstackptr;
- operator *stack = alloca(datasizes * sizeof(operator)), *stackptr = stack;
+ const char *p = endexpression;
- *errcode = 0;
- numstack = alloca((datasizes/2+1)*sizeof(long)), numstackptr = numstack;
+ size_t datasizes = strlen(expr);
- while ((arithval = *expr)) {
- if (arithval == ' ' || arithval == '\n' || arithval == '\t')
- goto prologue;
+ /* Stack of integers */
+ /* The proof that there can be no more than strlen(startbuf)/2+1 integers
+ * in any given correct or incorrect expression is left as an excersize to
+ * the reader. */
+ long *numstack = alloca((datasizes/2)*sizeof(long)),
+ *numstackptr = numstack;
+ /* Stack of operator tokens */
+ operator *stack = alloca((datasizes+1) * sizeof(operator)),
+ *stackptr = stack;
+
+ *stackptr++ = lasttok = TOK_LPAREN; /* start off with a left paren */
+
+ loop:
+ if ((arithval = *expr) == 0) {
+ if (p == endexpression) { /* Null expression. */
+ return (*errcode = 0);
+ }
+
+ /* This is only reached after all tokens have been extracted from the
+ * input stream. If there are still tokens on the operator stack, they
+ * are to be applied in order. At the end, there should be a final
+ * result on the integer stack */
+
+ if (expr != endexpression + 1) { /* If we haven't done so already, */
+ expr = endexpression; /* append a closing right paren */
+ goto loop; /* and let the loop process it. */
+ }
+ /* At this point, we're done with the expression. */
+ if (numstackptr != numstack+1) {/* ... but if there isn't, it's bad */
+ err:
+ return (*errcode = -1);
+ /* NOTREACHED */
+ }
+ return *numstack;
+ } else {
+ /* Continue processing the expression. */
+ if (isspace(arithval)) {
+ goto prologue; /* Skip whitespace */
+ }
if ((unsigned)arithval-'0' <= 9) /* isdigit */ {
*numstackptr++ = strtol(expr, (char **) &expr, 10);
lasttok = TOK_NUM;
- continue;
- } if (arithval == '(') {
- *stackptr++ = TOK_LPAREN;
- lasttok = TOK_LPAREN;
- goto prologue;
- } if (arithval == ')') {
- lasttok = TOK_NUM;
- while (stackptr != stack) {
- op = *--stackptr;
- if (op == TOK_LPAREN)
- goto prologue;
- *errcode = ARITH_APPLY(op);
- if(*errcode) return *errcode;
- }
- goto err; /* Mismatched parens */
- } if (arithval == '|') {
- if (*++expr == '|')
- op = TOK_OR;
- else {
- --expr;
- op = TOK_BOR;
- }
- } else if (arithval == '&') {
- if (*++expr == '&')
- op = TOK_AND;
- else {
- --expr;
- op = TOK_BAND;
+ goto loop;
+ }
+#if 1
+ if ((p = strchr(op_char, arithval)) == NULL) {
+ goto err;
+ }
+#else
+ for ( p=op_char ; *p != arithval ; p++ ) {
+ if (!*p) {
+ goto err;
}
- } else if (arithval == '=') {
- if (*++expr != '=') goto err; /* Unknown token */
- op = TOK_EQ;
- } else if (arithval == '!') {
- if (*++expr == '=')
- op = TOK_NE;
- else {
+ }
+#endif
+ p = op_token + (int)(p - op_char);
+ ++expr;
+ if ((p >= op_token + NUM_PAIR_EQUAL) || (*expr != '=')) {
+ p += NUM_PAIR_EQUAL;
+ if ((p >= op_token + NUM_PAIR_SAME + NUM_PAIR_EQUAL)
+ || (*expr != arithval) || (arithval == '!')) {
--expr;
- op = TOK_NOT;
- }
- } else if (arithval == '>') {
- switch (*++expr) {
- case '=':
- op = TOK_GE;
- break;
- case '>':
- op = TOK_RSHIFT;
- break;
- default:
- --expr;
- op = TOK_GT;
+ if (arithval == '=') { /* single = */
+ goto err;
+ }
+ p += NUM_PAIR_SAME;
+ /* Plus and minus are binary (not unary) _only_ if the last
+ * token was as number, or a right paren (which pretends to be
+ * a number, since it evaluates to one). Think about it.
+ * It makes sense. */
+ if ((lasttok != TOK_NUM)
+ && (p >= op_token + NUM_PAIR_SAME + NUM_PAIR_EQUAL
+ + sizeof(op_char) - 2)) {
+ p += 2; /* Unary plus or minus */
+ }
}
- } else if (arithval == '<') {
- switch (*++expr) {
- case '=':
- op = TOK_LE;
- break;
- case '<':
- op = TOK_LSHIFT;
- break;
- default:
- --expr;
- op = TOK_LT;
- }
- } else if (arithval == '*')
- op = TOK_MUL;
- else if (arithval == '/')
- op = TOK_DIV;
- else if (arithval == '%')
- op = TOK_REM;
- else if (arithval == '+') {
- if (lasttok != TOK_NUM) goto prologue; /* Unary plus */
- op = TOK_ADD;
- } else if (arithval == '-')
- op = (lasttok == TOK_NUM) ? TOK_SUB : TOK_UMINUS;
- else if (arithval == '~')
- op = TOK_BNOT;
- else goto err; /* Unknown token */
+ }
+ op = *p;
+ /* We don't want a 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
+ * 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
+ * "applied" in this way */
prec = PREC(op);
- if (prec != UNARYPREC)
- while (stackptr != stack && PREC(stackptr[-1]) >= prec) {
+ if ((prec > 0) && (prec != UNARYPREC)) { /* not left paren or unary */
+ if (lasttok != TOK_NUM) { /* binary op must be preceded by a num */
+ goto err;
+ }
+ while (stackptr != stack) {
+ if (op == TOK_RPAREN) {
+ /* The algorithm employed here is simple: while we don't
+ * hit an open paren nor the bottom of the stack, pop
+ * tokens and apply them */
+ if (stackptr[-1] == TOK_LPAREN) {
+ --stackptr;
+ lasttok = TOK_NUM; /* Any operator directly after a */
+ /* close paren should consider itself binary */
+ goto prologue;
+ }
+ } else if (PREC(stackptr[-1]) < prec) {
+ break;
+ }
*errcode = ARITH_APPLY(*--stackptr);
if(*errcode) return *errcode;
}
- *stackptr++ = op;
- lasttok = op;
-prologue: ++expr;
- } /* yay */
-
- while (stackptr != stack) {
- *errcode = ARITH_APPLY(*--stackptr);
- if(*errcode) return *errcode;
- }
- if (numstackptr != numstack+1) {
-err:
- *errcode = -1;
- return -1;
- /* NOTREACHED */
- }
+ if (op == TOK_RPAREN) {
+ goto err;
+ }
+ }
- return *numstack;
+ /* Push this operator to the stack and remember it. */
+ *stackptr++ = lasttok = op;
+
+ prologue:
+ ++expr;
+ goto loop;
+ }
}
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