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/* |
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ntom.c: N->M down/up sampling; the setup code. |
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copyright 1995-2008 by the mpg123 project - free software under the terms of the LGPL 2.1 |
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see COPYING and AUTHORS files in distribution or http://mpg123.org |
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initially written by Michael Hipp |
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*/ |
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#define SAFE_NTOM /* Do not depend on off_t*off_t with big values still being in the range... */ |
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#include "mpg123lib_intern.h" |
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#include "debug.h" |
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int synth_ntom_set_step(mpg123_handle *fr) |
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{ |
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long m,n; |
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m = frame_freq(fr); |
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n = fr->af.rate; |
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if(VERBOSE2) |
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fprintf(stderr,"Init rate converter: %ld->%ld\n",m,n); |
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if(n > NTOM_MAX_FREQ || m > NTOM_MAX_FREQ || m <= 0 || n <= 0) { |
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if(NOQUIET) error("NtoM converter: illegal rates"); |
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fr->err = MPG123_BAD_RATE; |
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return -1; |
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} |
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n *= NTOM_MUL; |
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fr->ntom_step = (unsigned long) n / m; |
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if(fr->ntom_step > (unsigned long)NTOM_MAX*NTOM_MUL) { |
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if(NOQUIET) error3("max. 1:%i conversion allowed (%lu vs %lu)!", NTOM_MAX, fr->ntom_step, (unsigned long)8*NTOM_MUL); |
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fr->err = MPG123_BAD_RATE; |
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return -1; |
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} |
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fr->ntom_val[0] = fr->ntom_val[1] = ntom_val(fr, fr->num); |
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return 0; |
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} |
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/* |
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The SAFE_NTOM does iterative loops instead of straight multiplication. |
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The safety is not just about the algorithm closely mimicking the decoder instead of applying some formula, |
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it is more about avoiding multiplication of possibly big sample offsets (a 32bit off_t could overflow too easily). |
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*/ |
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unsigned long ntom_val(mpg123_handle *fr, off_t frame) |
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{ |
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off_t ntm; |
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#ifdef SAFE_NTOM /* Carry out the loop, without the threatening integer overflow. */ |
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off_t f; |
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ntm = NTOM_MUL>>1; /* for frame 0 */ |
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for(f=0; f 0 */ |
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{ |
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ntm += spf(fr)*fr->ntom_step; |
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ntm -= (ntm/NTOM_MUL)*NTOM_MUL; |
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} |
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#else /* Just make one computation with overall sample offset. */ |
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ntm = (NTOM_MUL>>1) + spf(fr)*frame*fr->ntom_step; |
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ntm -= (ntm/NTOM_MUL)*NTOM_MUL; |
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#endif |
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return (unsigned long) ntm; |
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} |
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/* Set the ntom value for next expected frame to be decoded. |
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This is for keeping output consistent across seeks. */ |
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void ntom_set_ntom(mpg123_handle *fr, off_t num) |
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{ |
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fr->ntom_val[1] = fr->ntom_val[0] = ntom_val(fr, num); |
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} |
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/* Carry out the ntom sample count operation for this one frame. |
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No fear of integer overflow here. */ |
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off_t ntom_frame_outsamples(mpg123_handle *fr) |
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{ |
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/* The do this before decoding the separate channels, so there is only one common ntom value. */ |
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int ntm = fr->ntom_val[0]; |
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ntm += spf(fr)*fr->ntom_step; |
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return ntm/NTOM_MUL; |
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} |
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/* Convert frame offset to unadjusted output sample offset. */ |
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off_t ntom_frmouts(mpg123_handle *fr, off_t frame) |
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{ |
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#ifdef SAFE_NTOM |
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off_t f; |
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#endif |
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off_t soff = 0; |
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off_t ntm = ntom_val(fr,0); |
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#ifdef SAFE_NTOM |
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if(frame <= 0) return 0; |
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for(f=0; f |
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{ |
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ntm += spf(fr)*fr->ntom_step; |
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soff += ntm/NTOM_MUL; |
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ntm -= (ntm/NTOM_MUL)*NTOM_MUL; |
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} |
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#else |
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soff = (ntm + frame*(off_t)spf(fr)*(off_t)fr->ntom_step)/(off_t)NTOM_MUL; |
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#endif |
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return soff; |
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} |
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/* Convert input samples to unadjusted output samples. */ |
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off_t ntom_ins2outs(mpg123_handle *fr, off_t ins) |
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{ |
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off_t soff = 0; |
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off_t ntm = ntom_val(fr,0); |
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#ifdef SAFE_NTOM |
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{ |
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off_t block = spf(fr); |
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if(ins <= 0) return 0; |
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do |
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{ |
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off_t nowblock = ins > block ? block : ins; |
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ntm += nowblock*fr->ntom_step; |
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soff += ntm/NTOM_MUL; |
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ntm -= (ntm/NTOM_MUL)*NTOM_MUL; |
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ins -= nowblock; |
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} while(ins > 0); |
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} |
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#else |
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/* Beware of overflows: when off_t is 32bits, the multiplication blows too easily. |
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Of course, it blows for 64bits, too, in theory, but that's for _really_ large files. */ |
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soff = ((off_t)ntm + (off_t)ins*(off_t)fr->ntom_step)/(off_t)NTOM_MUL; |
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#endif |
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return soff; |
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} |
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/* Determine frame offset from unadjusted output sample offset. */ |
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off_t ntom_frameoff(mpg123_handle *fr, off_t soff) |
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{ |
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off_t ioff = 0; /* frames or samples */ |
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off_t ntm = ntom_val(fr,0); |
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#ifdef SAFE_NTOM |
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if(soff <= 0) return 0; |
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for(ioff=0; 1; ++ioff) |
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{ |
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ntm += spf(fr)*fr->ntom_step; |
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if(ntm/NTOM_MUL > soff) break; |
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soff -= ntm/NTOM_MUL; |
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ntm -= (ntm/NTOM_MUL)*NTOM_MUL; |
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} |
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return ioff; |
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#else |
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ioff = (soff*(off_t)NTOM_MUL-ntm)/(off_t)fr->ntom_step; |
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return ioff/(off_t)spf(fr); |
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#endif |
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} |