gh-112301: Use literal format strings in unicode_fromformat_arg (GH-124203)

Author: encukou

Objects/unicodeobject.c

@@ -2694,11 +2694,6 @@ unicode_fromformat_write_wcstr(_PyUnicodeWriter *writer, const wchar_t *str,
 #define F_SIZE 3
 #define F_PTRDIFF 4
 #define F_INTMAX 5
-static const char * const formats[] = {"%d", "%ld", "%lld", "%zd", "%td", "%jd"};
-static const char * const formats_o[] = {"%o", "%lo", "%llo", "%zo", "%to", "%jo"};
-static const char * const formats_u[] = {"%u", "%lu", "%llu", "%zu", "%tu", "%ju"};
-static const char * const formats_x[] = {"%x", "%lx", "%llx", "%zx", "%tx", "%jx"};
-static const char * const formats_X[] = {"%X", "%lX", "%llX", "%zX", "%tX", "%jX"};
 
 static const char*
 unicode_fromformat_arg(_PyUnicodeWriter *writer,
@@ -2840,47 +2835,44 @@ unicode_fromformat_arg(_PyUnicodeWriter *writer,
     case 'd': case 'i':
     case 'o': case 'u': case 'x': case 'X':
     {
-        /* used by sprintf */
         char buffer[MAX_INTMAX_CHARS];
-        const char *fmt = NULL;
-        switch (*f) {
-            case 'o': fmt = formats_o[sizemod]; break;
-            case 'u': fmt = formats_u[sizemod]; break;
-            case 'x': fmt = formats_x[sizemod]; break;
-            case 'X': fmt = formats_X[sizemod]; break;
-            default: fmt = formats[sizemod]; break;
-        }
-        int issigned = (*f == 'd' || *f == 'i');
+
+        // Fill buffer using sprinf, with one of many possible format
+        // strings, like "%llX" for `long long` in hexadecimal.
+        // The type/size is in `sizemod`; the format is in `*f`.
+
+        // Use macros with nested switches to keep the sprintf format strings
+        // as compile-time literals, avoiding warnings and maybe allowing
+        // optimizations.
+
+        // `SPRINT` macro does one sprintf
+        // Example usage: SPRINT("l", "X", unsigned long) expands to
+        // sprintf(buffer, "%" "l" "X", va_arg(*vargs, unsigned long))
+        #define SPRINT(SIZE_SPEC, FMT_CHAR, TYPE) \
+            sprintf(buffer, "%" SIZE_SPEC FMT_CHAR, va_arg(*vargs, TYPE))
+
+        // One inner switch to handle all format variants
+        #define DO_SPRINTS(SIZE_SPEC, SIGNED_TYPE, UNSIGNED_TYPE)             \
+            switch (*f) {                                                     \
+                case 'o': len = SPRINT(SIZE_SPEC, "o", UNSIGNED_TYPE); break; \
+                case 'u': len = SPRINT(SIZE_SPEC, "u", UNSIGNED_TYPE); break; \
+                case 'x': len = SPRINT(SIZE_SPEC, "x", UNSIGNED_TYPE); break; \
+                case 'X': len = SPRINT(SIZE_SPEC, "X", UNSIGNED_TYPE); break; \
+                default:  len = SPRINT(SIZE_SPEC, "d", SIGNED_TYPE); break;   \
+            }
+
+        // Outer switch to handle all the sizes/types
         switch (sizemod) {
-            case F_LONG:
-                len = issigned ?
-                    sprintf(buffer, fmt, va_arg(*vargs, long)) :
-                    sprintf(buffer, fmt, va_arg(*vargs, unsigned long));
-                break;
-            case F_LONGLONG:
-                len = issigned ?
-                    sprintf(buffer, fmt, va_arg(*vargs, long long)) :
-                    sprintf(buffer, fmt, va_arg(*vargs, unsigned long long));
-                break;
-            case F_SIZE:
-                len = issigned ?
-                    sprintf(buffer, fmt, va_arg(*vargs, Py_ssize_t)) :
-                    sprintf(buffer, fmt, va_arg(*vargs, size_t));
-                break;
-            case F_PTRDIFF:
-                len = sprintf(buffer, fmt, va_arg(*vargs, ptrdiff_t));
-                break;
-            case F_INTMAX:
-                len = issigned ?
-                    sprintf(buffer, fmt, va_arg(*vargs, intmax_t)) :
-                    sprintf(buffer, fmt, va_arg(*vargs, uintmax_t));
-                break;
-            default:
-                len = issigned ?
-                    sprintf(buffer, fmt, va_arg(*vargs, int)) :
-                    sprintf(buffer, fmt, va_arg(*vargs, unsigned int));
-                break;
+            case F_LONG:     DO_SPRINTS("l", long, unsigned long); break;
+            case F_LONGLONG: DO_SPRINTS("ll", long long, unsigned long long); break;
+            case F_SIZE:     DO_SPRINTS("z", Py_ssize_t, size_t); break;
+            case F_PTRDIFF:  DO_SPRINTS("t", ptrdiff_t, ptrdiff_t); break;
+            case F_INTMAX:   DO_SPRINTS("j", intmax_t, uintmax_t); break;
+            default:         DO_SPRINTS("", int, unsigned int); break;
         }
+        #undef SPRINT
+        #undef DO_SPRINTS
+
         assert(len >= 0);
 
         int sign = (buffer[0] == '-');