simplify copyBytes excess calc and do sseek()

examples/middle_amp.scri

@@ -1,3 +1,3 @@
 load :0;
-amp 3 1 10;
+amp 3 1 20;
 quicksave;

src/image.zig

@@ -54,12 +54,10 @@ fn swrite(file: *c.SNDFILE, buf: [*]f32, frames: i64) !void {
     }
 }
 
-fn sseek(file: *c.SNDFILE, offset: usize) !void {
+fn sseek(file: *c.SNDFILE, offset: usize) void {
     const frames = c.sf_seek(file, @intCast(i64, offset), c.SEEK_SET);
-
     if (frames != @intCast(i64, offset)) {
         std.debug.warn("failed to seek to {}\n", offset);
-        return error.SeekFail;
     }
 }
 
@@ -187,24 +185,22 @@ pub const Image = struct {
 
         // we do sf_seek() calls to make sure we are actually on the start
         // and actually end at the end position for the file.
-        try sseek(self.sndfile, start);
-        try sseek(out_file, start);
+        sseek(self.sndfile, start);
+        sseek(out_file, start);
 
         while (i <= end) : (i += buf.len) {
             std.debug.warn("i={}, buf.len={}, end={}\n", i, buf.len, end);
-            const excess = @intCast(i64, i + buf.len) - @intCast(i64, end);
+            sseek(self.sndfile, i);
+            sseek(out_file, i);
+
+            const bytes_until_end = end - i;
 
             var read_bytes: i64 = undefined;
             var view: []f32 = buf[0..buf.len];
 
-            if (excess > 0) {
-                std.debug.warn(
-                    "excess of {} bytes, reading {} instead\n",
-                    excess,
-                    @intCast(i64, buf.len) - excess,
-                );
-                read_bytes = c.sf_readf_float(self.sndfile, buf.ptr, @intCast(i64, buf.len) - excess);
-                view = buf[0..@intCast(usize, excess)];
+            if (bytes_until_end < buf.len) {
+                read_bytes = c.sf_readf_float(self.sndfile, buf.ptr, @intCast(i64, bytes_until_end));
+                view = buf[0..bytes_until_end];
             } else {
                 read_bytes = c.sf_readf_float(self.sndfile, buf.ptr, @intCast(i64, buf.len));
             }
@@ -212,8 +208,8 @@ pub const Image = struct {
             try swrite(out_file, view.ptr, @intCast(i64, view.len));
         }
 
-        try sseek(self.sndfile, end);
-        try sseek(out_file, end);
+        sseek(self.sndfile, end);
+        sseek(out_file, end);
     }
 
     fn getSeekPos(self: *Image, position: plugins.Position) plugins.SeekPos {
@@ -304,7 +300,7 @@ pub const Image = struct {
             seek_pos.start,
         );
 
-        try sseek(self.sndfile, seek_pos.start);
+        sseek(self.sndfile, seek_pos.start);
 
         var i: usize = seek_pos.start;
         std.debug.warn("\tseek pos start: {} end: {}\n", seek_pos.start, seek_pos.end);
@@ -323,7 +319,7 @@ pub const Image = struct {
             try swrite(out_file, outbuf.ptr, 1);
         }
 
-        try sseek(self.sndfile, seek_pos.end);
+        sseek(self.sndfile, seek_pos.end);
 
         // post-plugin copy
         try self.copyBytes(
@@ -368,7 +364,7 @@ pub const Image = struct {
         const seek_pos = self.getSeekPos(position);
 
         // make sure we start from 0
-        try sseek(self.sndfile, 0);
+        sseek(self.sndfile, 0);
 
         // there are four main stages:
         // - the bmp header copy
@@ -383,7 +379,7 @@ pub const Image = struct {
             seek_pos.start,
         );
 
-        try sseek(self.sndfile, seek_pos.start);
+        sseek(self.sndfile, seek_pos.start);
 
         var i: usize = seek_pos.start;
         std.debug.warn("\tseek pos start: {} end: {}\n", seek_pos.start, seek_pos.end);
@@ -402,7 +398,7 @@ pub const Image = struct {
             try swrite(out_file, bufs.out.ptr, 1);
         }
 
-        try sseek(self.sndfile, seek_pos.end);
+        sseek(self.sndfile, seek_pos.end);
 
         // post-plugin copy
         try self.copyBytes(