avformat/mpsubdec: Remove floating point usage

This makes the code bitexact between platforms.
Intermediate timestamps between frames are preserved.
The timebase is simplified.
Rounding differs from doubles in cases where timestamps/durations
are "funny"

Suggested-by: jb
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mpsubdec.c

@@ -27,6 +27,8 @@
 #include "internal.h"
 #include "subtitles.h"
 
+#define TSBASE 10000000
+
 typedef struct {
     FFDemuxSubtitlesQueue q;
 } MPSubContext;
@@ -51,21 +53,55 @@ static int mpsub_probe(const AVProbeData *p)
     return 0;
 }
 
+static int parse_line(const char *line, int64_t *value, int64_t *value2)
+{
+    int vi, p1, p2;
+
+    for (vi = 0; vi < 2; vi++) {
+        long long intval, fracval;
+        int n = av_sscanf(line, "%lld%n.%lld%n", &intval, &p1, &fracval, &p2);
+        if (n <= 0 || intval < INT64_MIN / TSBASE || intval > INT64_MAX / TSBASE)
+            return AVERROR_INVALIDDATA;
+
+        intval *= TSBASE;
+
+        if (n == 2) {
+            if (fracval < 0)
+                return AVERROR_INVALIDDATA;
+            for (;p2 - p1 < 7 + 1; p1--)
+                fracval *= 10;
+            for (;p2 - p1 > 7 + 1; p1++)
+                fracval /= 10;
+            if (intval > 0) intval += fracval;
+            else            intval -= fracval;
+            line += p2;
+        } else
+            line += p1;
+
+        *value = intval;
+
+        value = value2;
+    }
+
+    return 0;
+}
+
 static int mpsub_read_header(AVFormatContext *s)
 {
     MPSubContext *mpsub = s->priv_data;
     AVStream *st;
     AVBPrint buf;
-    AVRational pts_info = (AVRational){ 100, 1 }; // ts based by default
+    AVRational pts_info = (AVRational){ TSBASE, 1 }; // ts based by default
     int res = 0;
-    int multiplier = 100;
-    double current_pts = 0;
+    int64_t current_pts = 0;
+    int i;
+    int common_factor = 0;
 
     av_bprint_init(&buf, 0, AV_BPRINT_SIZE_UNLIMITED);
 
     while (!avio_feof(s->pb)) {
         char line[1024];
-        double start, duration;
+        int64_t start, duration;
         int fps, len = ff_get_line(s->pb, line, sizeof(line));
 
         if (!len)
@@ -75,34 +111,48 @@ static int mpsub_read_header(AVFormatContext *s)
 
         if (sscanf(line, "FORMAT=%d", &fps) == 1 && fps > 3 && fps < 100) {
             /* frame based timing */
-            pts_info = (AVRational){ fps, 1 };
-            multiplier = 1;
-        } else if (sscanf(line, "%lf %lf", &start, &duration) == 2) {
+            pts_info = (AVRational){ TSBASE * fps, 1 };
+        } else if (parse_line(line, &start, &duration) >= 0) {
             AVPacket *sub;
             const int64_t pos = avio_tell(s->pb);
 
             ff_subtitles_read_chunk(s->pb, &buf);
             if (buf.len) {
-                double ts = current_pts + start*multiplier;
                 sub = ff_subtitles_queue_insert(&mpsub->q, buf.str, buf.len, 0);
                 if (!sub) {
                     res = AVERROR(ENOMEM);
                     goto end;
                 }
-                if (!isfinite(ts) || ts < INT64_MIN || ts > INT64_MAX) {
-                    avpriv_request_sample(s, "Invalid ts\n");
-                } else
-                    sub->pts = (int64_t)ts;
-                if (!isfinite(duration) || duration * multiplier > INT_MAX || duration < 0) {
-                    avpriv_request_sample(s, "Invalid duration\n");
-                } else
-                    sub->duration = (int)(duration * multiplier);
-                current_pts += (start + duration) * multiplier;
+                if (   current_pts < 0 && start < INT64_MIN - current_pts
+                    || current_pts > 0 && start > INT64_MAX - current_pts) {
+                    res = AVERROR_INVALIDDATA;
+                    goto end;
+                }
+                sub->pts = current_pts + start;
+                if (duration < 0 || sub->pts > INT64_MAX - duration) {
+                    res = AVERROR_INVALIDDATA;
+                    goto end;
+                }
+                sub->duration = duration;
+
+                common_factor = av_gcd(duration, common_factor);
+                common_factor = av_gcd(sub->pts, common_factor);
+
+                current_pts = sub->pts + duration;
                 sub->pos = pos;
             }
         }
     }
 
+    if (common_factor > 1) {
+        common_factor = av_gcd(pts_info.num, common_factor);
+        for (i = 0; i < mpsub->q.nb_subs; i++) {
+            mpsub->q.subs[i].pts      /= common_factor;
+            mpsub->q.subs[i].duration /= common_factor;
+        }
+        pts_info.num /= common_factor;
+    }
+
     st = avformat_new_stream(s, NULL);
     if (!st)
         return AVERROR(ENOMEM);

tests/ref/fate/sub-mpsub-frames

@@ -10,5 +10,5 @@ Style: Default,Arial,16,&Hffffff,&Hffffff,&H0,&H0,0,0,0,0,100,100,0,0,1,1,0,2,10
 
 [Events]
 Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
-Dialogue: 0,0:00:01.00,0:00:02.48,Default,,0,0,0,,Start at 1sec,\Nlast 1.5 seconds
-Dialogue: 0,0:00:02.52,0:00:11.52,Default,,0,0,0,,One frame later,\Nduring 9 seconds
+Dialogue: 0,0:00:01.00,0:00:02.50,Default,,0,0,0,,Start at 1sec,\Nlast 1.5 seconds
+Dialogue: 0,0:00:02.54,0:00:11.54,Default,,0,0,0,,One frame later,\Nduring 9 seconds