tinystdio: Fix vfprintf to not cap the max precision to print a hex format

newlib/libc/tinystdio/vfprintf.c

@@ -688,14 +688,24 @@ int vfprintf (FILE * stream, const CHAR *fmt, va_list ap_orig)
 #ifdef _NEED_IO_C99_FORMATS
                 if (c == 'a') {
 
+                    int init_prec = prec;
+
                     c = 'p';
                     flags |= FL_FLTEXP | FL_FLTHEX;
 
                     if (!(flags & FL_PREC))
                         prec = -1;
 
                     prec = __float_x_engine(fval, &dtoa, prec, case_convert);
+
+                    if(prec < init_prec)         /* if dtox engine capped the precision required */
+                    prec = init_prec;
+
                     ndigs = prec + 1;
+
+                    if(ndigs > 14)              /* the max dtox ndigs */
+                    ndigs = 14;
+
                     exp = dtoa.exp;
                     ndigs_exp = 1;
                 } else

test/meson.build

@@ -83,6 +83,7 @@ if (posix_io or not tinystdio) and tests_enable_posix_io
                     'test-fgetc',
                     'test-fgets-eof',
                     'test-wchar',
+                    'test-vfprintf-hex-prec'
                    ]
   endif
 endif

test/test-vfprintf-hex-prec.c

@@ -0,0 +1,62 @@
+/*
+* SPDX-License-Identifier: BSD-3-Clause
+* 
+* Copyright © 2024, Synopsys Inc.
+* Copyright © 2024, Solid Sands B.V.
+*
+* Redistribution and use in source and binary forms, with or without
+* modification, are permitted provided that the following conditions
+* are met:
+*
+* 1. Redistributions of source code must retain the above copyright
+*    notice, this list of conditions and the following disclaimer.
+*
+* 2. Redistributions in binary form must reproduce the above
+*    copyright notice, this list of conditions and the following
+*    disclaimer in the documentation and/or other materials provided
+*    with the distribution.
+*
+* 3. Neither the name of the copyright holder nor the names of its
+*    contributors may be used to endorse or promote products derived
+*    from this software without specific prior written permission.
+*
+* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+* COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
+* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+* OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#include <stdio.h>
+#include <string.h>
+
+int main(void) {
+    int res = 0;
+    int ret = 0;
+    size_t len = 0;
+    char strin[50];
+
+    res = sprintf(strin, "%.15A\n", 471.2853);
+
+    const char* ref_out = "0X1.D749096BB98C800P+8\n";
+    const int ref_len = 23;
+
+    ret = strcmp(strin, ref_out);
+    len = strlen(strin);
+
+    if ((res != ref_len) || (ret != 0) || (len != ref_len)) {
+        printf("Test Failed: Failed to read/write 15 digits after decimal point in hex format\n");
+        return 1;
+    }
+
+    printf("Test Passed\n");
+
+    return 0;
+}