diff options
author | Manuel Novoa III <mjn3@codepoet.org> | 2001-09-11 05:11:31 +0400 |
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committer | Manuel Novoa III <mjn3@codepoet.org> | 2001-09-11 05:11:31 +0400 |
commit | 6a9d1f652b20f53dfd64e260d2796d55ad973c98 (patch) | |
tree | a01f496c00bceef7c8fec6e2c3e80c473be020c5 /libbb | |
parent | f6ecaccf929c470b2eb4803af35df4ffaee497b1 (diff) |
Commit my changes to arith.c which fixed a couple of bugs and decreased
code size. Please read the TODO comments regarding accessing shell
variables from the arith() funciton.
Diffstat (limited to 'libbb')
-rw-r--r-- | libbb/arith.c | 396 |
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; + } } |