学步园

/* Main interpreter. */<br /> /* If execution terminates normally, return e_InterpreterExit. */<br /> /* If an error occurs, leave the current object in *perror_object */<br /> /* and return a (negative) error code. */<br /> static int<br /> interp(i_ctx_t **pi_ctx_p /* context for execution, updated if resched */,<br /> const ref * pref /* object to interpret */,<br /> ref * perror_object)<br /> {<br /> i_ctx_t *i_ctx_p = *pi_ctx_p;<br /> /*<br /> * Note that iref may actually be either a ref * or a ref_packed *.<br /> * Certain DEC compilers assume that a ref * is ref-aligned even if it<br /> * is cast to a short *, and generate code on this assumption, leading<br /> * to "unaligned access" errors. For this reason, we declare<br /> * iref_packed, and use a macro to cast it to the more aligned type<br /> * where necessary (which is almost everywhere it is used). This may<br /> * lead to compiler warnings about "cast increases alignment<br /> * requirements", but this is less harmful than expensive traps at run<br /> * time.<br /> */<br /> register const ref_packed *iref_packed = (const ref_packed *)pref;

interp函数的第二个参数是const ref* pref。

它来至于上层函数的调用：

下面的临时变量ref ifile;就是传入参数。

/* Open and run the very first initialization file. */<br /> static int<br /> gs_run_init_file(gs_main_instance * minst, int *pexit_code, ref * perror_object)<br /> {<br /> i_ctx_t *i_ctx_p = minst->i_ctx_p;<br /> ref ifile;<br /> ref first_token;<br /> int code;<br /> scanner_state state;</p> <p> gs_main_set_lib_paths(minst);<br /> code = gs_main_run_file_open(minst, gs_init_file, &ifile);<br /> if (code < 0) {<br /> *pexit_code = 255;<br /> return code;<br /> }<br /> /* Check to make sure the first token is an integer */<br /> /* (for the version number check.) */<br /> scanner_init(&state, &ifile);<br /> code = scan_token(i_ctx_p, &first_token, &state);<br /> if (code != 0 || !r_has_type(&first_token, t_integer)) {<br /> eprintf1("Initialization file %s does not begin with an integer./n", gs_init_file);<br /> *pexit_code = 255;<br /> return_error(e_Fatal);<br /> }<br /> *++osp = first_token;<br /> r_set_attrs(&ifile, a_executable);<br /> return gs_main_interpret(minst, &ifile, minst->user_errors,<br /> pexit_code, perror_object);<br /> }

这个参数在函数gs_main_run_file_open中被修改：

int<br /> gs_main_run_file_open(gs_main_instance * minst, const char *file_name, ref * pfref)<br /> {<br /> gs_main_set_lib_paths(minst);<br /> if (gs_main_lib_open(minst, file_name, pfref) < 0) {<br /> eprintf1("Can't find initialization file %s./n", file_name);<br /> return_error(e_Fatal);<br /> }<br /> r_set_attrs(pfref, a_execute + a_executable);<br /> return 0;<br /> }

被修改的语句是：

r_set_attrs(pfref, a_execute+a_executable);

而这句代码的实现为：

#define r_set_attrs(rp,mask) ((rp)->tas.type_attrs |= (mask))

也就是这个对象的type_attrs被修改了。而这个对象属性在interp函数中涉及到“分派”，是很重要的属性。

在gs_run_init_file （）中第一次调用scan_token()获得first_token，再把这个token放进操作符栈中。

 *++osp = first_token;这句实现这个功能。

后面还有一句：r_set_attrs(&ifile, a_executable);从这句调试来看这句并没有改别type_attrs的值。

这个ifile被传给interp函数之后，通过：

switch (r_type_xe(iref_packed))</p> <p>{</p> <p>..............................</p> <p>.............................</p> <p>case exec(t_file):<br /> { /* Executable file. Read the next token and interpret it. */<br /> stream *s;<br /> scanner_state sstate;</p> <p> check_read_known_file(s, IREF, return_with_error_iref);<br /> rt:<br /> if (iosp >= ostop) /* check early */<br /> return_with_stackoverflow_iref();<br /> osp = iosp; /* scan_token uses ostack */<br /> scanner_init_options(&sstate, IREF, i_ctx_p->scanner_options);<br /> again:<br /> code = scan_token(i_ctx_p, &token, &sstate);<br /> iosp = osp; /* ditto */<br /> switch (code) {<br /> case 0: /* read a token */<br /> /* It's worth checking for literals, which make up */<br /> /* the majority of input tokens, before storing the */<br /> /* state on the e-stack. Note that because of //, */<br /> /* the token may have *any* type and attributes. */<br /> /* Note also that executable arrays aren't executed */<br /> /* at the top level -- they're treated as literals. */<br /> if (!r_has_attr(&token, a_executable) ||<br /> r_is_array(&token)<br /> ) { /* If scan_token used the o-stack, */<br /> /* we know we can do a push now; if not, */<br /> /* the pre-check is still valid. */<br /> iosp++;<br /> ref_assign_inline(iosp, &token);<br /> goto rt;<br /> }<br /> store_state(iesp);</p> <p>....................</p> <p>......................</p> <p>}<br />

调用词法分析函数：scan_token()。

整个解析函数有两处调用scan_token()函数。

另外r_type_xe宏的实现在以前发过的文章关于iref.h中有讨论。