preproc: add a %selbits() function

Although one can implement this "manually" in terms of %sel(), this
function is *really* useful for making multi-mode tests and allows for
better error checking.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

asm/preproc.c

@@ -7738,9 +7738,9 @@ stdmac_tok(const SMacro *s, Token **params, int nparams)
     return reverse_tokens(tokenize(unquote_token_cstr(params[0])));
 }
 
-/* %cond() or %sel() */
+/* %sel() */
 static Token *
-stdmac_cond_sel(const SMacro *s, Token **params, int nparams)
+stdmac_sel(const SMacro *s, Token **params, int nparams)
 {
     int64_t which;
 
@@ -7749,14 +7749,6 @@ stdmac_cond_sel(const SMacro *s, Token **params, int nparams)
      */
     which = get_tok_num(params[0], NULL);
 
-    if (s->expandpvt.u) {
-        /* Booleanize (for %cond): true -> 1, false -> 2 (else) */
-        which = which ? 1 : 2;
-        if (which >= nparams) {
-            /* false, and no else clause */
-            return NULL;
-        }
-    } else {
     if (unlikely(which < 1)) {
         nasm_warn(WARN_PP_SEL_RANGE,
                   "%s(%"PRId64") is not a valid selector", s->name, which);
@@ -7767,11 +7759,47 @@ stdmac_cond_sel(const SMacro *s, Token **params, int nparams)
                   s->name, which);
         return NULL;
     }
+
+    return new_Token(NULL, tok_smac_param(which), "", 0);
+}
+
+/* %cond() */
+static Token *
+stdmac_cond(const SMacro *s, Token **params, int nparams)
+{
+    int64_t which;
+    (void)s;
+    (void)params;
+
+    /*
+     * params[0] will have been generated by make_tok_num.
+     */
+    which = get_tok_num(params[0], NULL);
+
+    /* Booleanize: true -> 1, false -> 2 (else) */
+    which = which ? 1 : 2;
+    if (which >= nparams) {
+        /* false, and no else clause */
+        return NULL;
     }
 
     return new_Token(NULL, tok_smac_param(which), "", 0);
 }
 
+/* %selbits() */
+static Token *
+stdmac_selbits(const SMacro *s, Token **params, int nparams)
+{
+    int which = ilog2_32(globl.bits)-4;
+    (void)s;
+    (void)params;
+
+    if (nparams <= which)
+        which = nparams - 1;
+
+    return new_Token(NULL, tok_smac_param(which), "", 0);
+}
+
 /* %count() function */
 static Token *
 stdmac_count(const SMacro *s, Token **params, int nparams)
@@ -8173,6 +8201,7 @@ static void pp_add_magic_simple(void)
         { "%null",       false, 1, SPARM_GREEDY, stdmac_null },
         { "%pathsearch", false, 1, SPARM_PLAIN, stdmac_pathsearch },
         { "%realpath",	 false, 1, SPARM_PLAIN, stdmac_realpath },
+        { "%selbits",    false, 1, SPARM_PLAIN|SPARM_VARADIC, stdmac_selbits },
         { "%str",        false, 1, SPARM_GREEDY|SPARM_STR, stdmac_join },
         { "%strcat",     false, 1, SPARM_STR|SPARM_CONDQUOTE|SPARM_VARADIC, stdmac_strcat },
         { "%strlen",     false, 1, SPARM_STR|SPARM_CONDQUOTE, stdmac_strlen },
@@ -8268,15 +8297,16 @@ static void pp_add_magic_miscfunc(void)
     /* %sel() function */
     nasm_zero(tmpl);
     tmpl.nparam    = 2;
-    tmpl.expand    = stdmac_cond_sel;
+    tmpl.expand    = stdmac_sel;
     nasm_newn(tmpl.params, tmpl.nparam);
     tmpl.params[0].flags = SPARM_EVAL;
     tmpl.params[1].flags = SPARM_VARADIC;
     define_magic("%sel", false, &tmpl);
 
-    /* %cond() function, a variation on %sel */
+    /* %cond() function */
+    nasm_zero(tmpl);
     tmpl.nparam = 3;
-    tmpl.expandpvt.u = 1;         /* Booleanize */
+    tmpl.expand = stdmac_cond;
     nasm_newn(tmpl.params, tmpl.nparam);
     tmpl.params[0].flags = SPARM_EVAL;
     tmpl.params[1].flags = 0;

doc/changes.src

@@ -31,6 +31,8 @@ It is the production version of NASM since 2025.
    now be specified for the same group; the resulting group includes
    all sections specified in all \c{GROUP} directives for the group.
 
+\b A new \c{%selbits()} preprocessor function.  See \k{f_selbits}.
+
 
 \S{cl-3.00} Version 3.00
 

doc/preproc.src

@@ -1011,6 +1011,24 @@ expands to nothing.
 The arguments not selected are never expanded.
 
 
+\S{f_selbits} \i\c{%selbits()} Function
+
+The \c{%selbits()} function returns its first, second, or third
+argument depending on if the current mode is 16, 32 or 64 bits. If
+less than three arguments are given, the last argument is considered
+repeated.  Like \c{%cond()}, this is a specialized version of the
+\c{%sel()} function.
+
+For example:
+
+\c      BITS 64
+\c
+\c %define breg %selbits(bx,ebx,rbx)
+\c %define vreg %selbits(ax,eax)
+\c
+\c      mov vreg,[breg]		; mov eax,[rbx]
+
+
 \S{f_str} \i\c\{%str()} Function
 
 The \c{%str()} function converts its argument, including any commas,