exprlib.c

nasm早期的源代码,比较简单是学习汇编和编译原理的好例子

/*
 * exprlib.c
 *
 * Library routines to manipulate expression data types.
 */

#include "nasm.h"

/*
 * Return true if the argument is a simple scalar. (Or a far-
 * absolute, which counts.)
 */
int is_simple(expr * vect)
{
    while (vect->type && !vect->value)
        vect++;
    if (!vect->type)
        return 1;
    if (vect->type != EXPR_SIMPLE)
        return 0;
    do {
        vect++;
    } while (vect->type && !vect->value);
    if (vect->type && vect->type < EXPR_SEGBASE + SEG_ABS)
        return 0;
    return 1;
}

/*
 * Return true if the argument is a simple scalar, _NOT_ a far-
 * absolute.
 */
int is_really_simple(expr * vect)
{
    while (vect->type && !vect->value)
        vect++;
    if (!vect->type)
        return 1;
    if (vect->type != EXPR_SIMPLE)
        return 0;
    do {
        vect++;
    } while (vect->type && !vect->value);
    if (vect->type)
        return 0;
    return 1;
}

/*
 * Return true if the argument is relocatable (i.e. a simple
 * scalar, plus at most one segment-base, plus possibly a WRT).
 */
int is_reloc(expr * vect)
{
    while (vect->type && !vect->value)  /* skip initial value-0 terms */
        vect++;
    if (!vect->type)            /* trivially return true if nothing */
        return 1;               /* is present apart from value-0s */
    if (vect->type < EXPR_SIMPLE)       /* false if a register is present */
        return 0;
    if (vect->type == EXPR_SIMPLE) {    /* skip over a pure number term... */
        do {
            vect++;
        } while (vect->type && !vect->value);
        if (!vect->type)        /* ...returning true if that's all */
            return 1;
    }
    if (vect->type == EXPR_WRT) {       /* skip over a WRT term... */
        do {
            vect++;
        } while (vect->type && !vect->value);
        if (!vect->type)        /* ...returning true if that's all */
            return 1;
    }
    if (vect->value != 0 && vect->value != 1)
        return 0;               /* segment base multiplier non-unity */
    do {                        /* skip over _one_ seg-base term... */
        vect++;
    } while (vect->type && !vect->value);
    if (!vect->type)            /* ...returning true if that's all */
        return 1;
    return 0;                   /* And return false if there's more */
}

/*
 * Return true if the argument contains an `unknown' part.
 */
int is_unknown(expr * vect)
{
    while (vect->type && vect->type < EXPR_UNKNOWN)
        vect++;
    return (vect->type == EXPR_UNKNOWN);
}

/*
 * Return true if the argument contains nothing but an `unknown'
 * part.
 */
int is_just_unknown(expr * vect)
{
    while (vect->type && !vect->value)
        vect++;
    return (vect->type == EXPR_UNKNOWN);
}

/*
 * Return the scalar part of a relocatable vector. (Including
 * simple scalar vectors - those qualify as relocatable.)
 */
int64_t reloc_value(expr * vect)
{
    while (vect->type && !vect->value)
        vect++;
    if (!vect->type)
        return 0;
    if (vect->type == EXPR_SIMPLE)
        return vect->value;
    else
        return 0;
}

/*
 * Return the segment number of a relocatable vector, or NO_SEG for
 * simple scalars.
 */
int32_t reloc_seg(expr * vect)
{
    while (vect->type && (vect->type == EXPR_WRT || !vect->value))
        vect++;
    if (vect->type == EXPR_SIMPLE) {
        do {
            vect++;
        } while (vect->type && (vect->type == EXPR_WRT || !vect->value));
    }
    if (!vect->type)
        return NO_SEG;
    else
        return vect->type - EXPR_SEGBASE;
}

/*
 * Return the WRT segment number of a relocatable vector, or NO_SEG
 * if no WRT part is present.
 */
int32_t reloc_wrt(expr * vect)
{
    while (vect->type && vect->type < EXPR_WRT)
        vect++;
    if (vect->type == EXPR_WRT) {
        return vect->value;
    } else
        return NO_SEG;
}