Issue-#3407 : Enhance precision for double to string conversion, useful for GEOTIFF double values

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/tiff.c

@@ -195,7 +195,7 @@ static char *doubles2str(double *dp, int count, const char *sep)
     char *ap, *ap0;
     uint64_t component_len;
     if (!sep) sep = ", ";
-    component_len = 15LL + strlen(sep);
+    component_len = 24LL + strlen(sep);
     if (count >= (INT_MAX - 1)/component_len)
         return NULL;
     ap = av_malloc(component_len * count + 1);
@@ -204,7 +204,7 @@ static char *doubles2str(double *dp, int count, const char *sep)
     ap0   = ap;
     ap[0] = '\0';
     for (i = 0; i < count; i++) {
-        unsigned l = snprintf(ap, component_len, "%f%s", dp[i], sep);
+        unsigned l = snprintf(ap, component_len, "%.15g%s", dp[i], sep);
         if(l >= component_len) {
             av_free(ap0);
             return NULL;

libavcodec/tiff_common.c

@@ -165,7 +165,7 @@ int ff_tadd_doubles_metadata(int count, const char *name, const char *sep,
     av_bprint_init(&bp, 10 * count, 100 * count);
 
     for (i = 0; i < count; i++) {
-        av_bprintf(&bp, "%s%f", auto_sep(count, sep, i, 4), ff_tget_double(gb, le));
+        av_bprintf(&bp, "%s%.15g", auto_sep(count, sep, i, 4), ff_tget_double(gb, le));
     }
 
     if ((i = av_bprint_finalize(&bp, &ap))) {