speed up the bounds checking in FLAC__encoder_process*

diff --git a/src/libFLAC/encoder.c b/src/libFLAC/encoder.c
index 255ab28..4ac3883 100644 (file)
--- a/src/libFLAC/encoder.c
+++ b/src/libFLAC/encoder.c
@@ -514,8 +514,7 @@ bool FLAC__encoder_process(FLAC__Encoder *encoder, const int32 *buf[], unsigned
        int32 x, mid, side;
        bool ms;
        const bool ms0 = encoder->do_mid_side_stereo && encoder->channels == 2;
-       const int32 min_side = -((int64)1 << (encoder->bits_per_sample-1));
-       const int32 max_side =  ((int64)1 << (encoder->bits_per_sample-1)) - 1;
+       const int32 limitmask = (int32)(((uint32)(-1)) >> (33-encoder->bits_per_sample));
        const unsigned channels = encoder->channels, blocksize = encoder->blocksize;
 
        assert(encoder != 0);
@@ -532,7 +531,7 @@ bool FLAC__encoder_process(FLAC__Encoder *encoder, const int32 *buf[], unsigned
                        }
                        if(ms) {
                                side = buf[0][j] - x; /* x still == buf[1][j] */
-                               if(side < min_side || side > max_side) {
+                               if(side & limitmask && ~side & limitmask) {
                                        encoder->guts->current_frame_can_do_mid_side = false;
                                        ms = false;
                                }
@@ -561,28 +560,30 @@ bool FLAC__encoder_process_interleaved(FLAC__Encoder *encoder, const int32 buf[]
 {
        unsigned i, j, k, channel;
        int32 x, left = 0, mid, side;
-       const bool ms = encoder->do_mid_side_stereo && encoder->channels == 2;
-       const int32 min_side = -((int64)1 << (encoder->bits_per_sample-1));
-       const int32 max_side =  ((int64)1 << (encoder->bits_per_sample-1)) - 1;
+       bool ms;
+       const bool ms0 = encoder->do_mid_side_stereo && encoder->channels == 2;
+       const int32 limitmask = (int32)(((uint32)(-1)) >> (33-encoder->bits_per_sample));
 
        assert(encoder != 0);
        assert(encoder->state == FLAC__ENCODER_OK);
 
        j = k = 0;
+       ms = ms0 && encoder->guts->current_frame_can_do_mid_side;
        do {
                for(i = encoder->guts->current_sample_number; i < encoder->blocksize && j < samples; i++, j++) {
                        for(channel = 0; channel < encoder->channels; channel++) {
                                x = buf[k++];
                                encoder->guts->integer_signal[channel][i] = x;
                                encoder->guts->real_signal[channel][i] = (real)x;
-                               if(ms && encoder->guts->current_frame_can_do_mid_side) {
+                               if(ms) {
                                        if(channel == 0) {
                                                left = x;
                                        }
                                        else {
                                                side = left - x;
-                                               if(side < min_side || side > max_side) {
+                                               if(side & limitmask && ~side & limitmask) {
                                                        encoder->guts->current_frame_can_do_mid_side = false;
+                                                       ms = false;
                                                }
                                                else {
                                                        mid = (left + x) >> 1; /* NOTE: not the same as 'mid = (left + x) / 2' ! */
@@ -599,6 +600,7 @@ bool FLAC__encoder_process_interleaved(FLAC__Encoder *encoder, const int32 buf[]
                if(i == encoder->blocksize) {
                        if(!encoder_process_frame_(encoder, false)) /* false => not last frame */
                                return false;
+                       ms = ms0;
                }
        } while(j < samples);