1 /* 2 ntom.c: N->M down/up sampling; the setup code. 3 4 copyright 1995-2008 by the mpg123 project - free software under the terms of the LGPL 2.1 5 see COPYING and AUTHORS files in distribution or http://mpg123.org 6 initially written by Michael Hipp 7 */ 8 9 #define SAFE_NTOM /* Do not depend on off_t*off_t with big values still being in the range... */ 10 #include "mpg123lib_intern.h" 11 #include "debug.h" 12 13 int synth_ntom_set_step(mpg123_handle *fr) 14 { 15 long m,n; 16 m = frame_freq(fr); 17 n = fr->af.rate; 18 if(VERBOSE2) 19 fprintf(stderr,"Init rate converter: %ld->%ld\n",m,n); 20 21 if(n > NTOM_MAX_FREQ || m > NTOM_MAX_FREQ || m <= 0 || n <= 0) { 22 if(NOQUIET) error("NtoM converter: illegal rates"); 23 fr->err = MPG123_BAD_RATE; 24 return -1; 25 } 26 27 n *= NTOM_MUL; 28 fr->ntom_step = (unsigned long) n / m; 29 30 if(fr->ntom_step > (unsigned long)NTOM_MAX*NTOM_MUL) { 31 if(NOQUIET) error3("max. 1:%i conversion allowed (%lu vs %lu)!", NTOM_MAX, fr->ntom_step, (unsigned long)8*NTOM_MUL); 32 fr->err = MPG123_BAD_RATE; 33 return -1; 34 } 35 36 fr->ntom_val[0] = fr->ntom_val[1] = ntom_val(fr, fr->num); 37 return 0; 38 } 39 40 /* 41 The SAFE_NTOM does iterative loops instead of straight multiplication. 42 The safety is not just about the algorithm closely mimicking the decoder instead of applying some formula, 43 it is more about avoiding multiplication of possibly big sample offsets (a 32bit off_t could overflow too easily). 44 */ 45 46 unsigned long ntom_val(mpg123_handle *fr, off_t frame) 47 { 48 off_t ntm; 49 #ifdef SAFE_NTOM /* Carry out the loop, without the threatening integer overflow. */ 50 off_t f; 51 ntm = NTOM_MUL>>1; /* for frame 0 */ 52 for(f=0; f<frame; ++f) /* for frame > 0 */ 53 { 54 ntm += fr->spf*fr->ntom_step; 55 ntm -= (ntm/NTOM_MUL)*NTOM_MUL; 56 } 57 #else /* Just make one computation with overall sample offset. */ 58 ntm = (NTOM_MUL>>1) + fr->spf*frame*fr->ntom_step; 59 ntm -= (ntm/NTOM_MUL)*NTOM_MUL; 60 #endif 61 return (unsigned long) ntm; 62 } 63 64 /* Set the ntom value for next expected frame to be decoded. 65 This is for keeping output consistent across seeks. */ 66 void ntom_set_ntom(mpg123_handle *fr, off_t num) 67 { 68 fr->ntom_val[1] = fr->ntom_val[0] = ntom_val(fr, num); 69 } 70 71 /* Carry out the ntom sample count operation for this one frame. 72 No fear of integer overflow here. */ 73 off_t ntom_frame_outsamples(mpg123_handle *fr) 74 { 75 /* The do this before decoding the separate channels, so there is only one common ntom value. */ 76 int ntm = fr->ntom_val[0]; 77 ntm += fr->spf*fr->ntom_step; 78 return ntm/NTOM_MUL; 79 } 80 81 /* Convert frame offset to unadjusted output sample offset. */ 82 off_t ntom_frmouts(mpg123_handle *fr, off_t frame) 83 { 84 #ifdef SAFE_NTOM 85 off_t f; 86 #endif 87 off_t soff = 0; 88 off_t ntm = ntom_val(fr,0); 89 #ifdef SAFE_NTOM 90 if(frame <= 0) return 0; 91 for(f=0; f<frame; ++f) 92 { 93 ntm += fr->spf*fr->ntom_step; 94 soff += ntm/NTOM_MUL; 95 ntm -= (ntm/NTOM_MUL)*NTOM_MUL; 96 } 97 #else 98 soff = (ntm + frame*(off_t)fr->spf*(off_t)fr->ntom_step)/(off_t)NTOM_MUL; 99 #endif 100 return soff; 101 } 102 103 /* Convert input samples to unadjusted output samples. */ 104 off_t ntom_ins2outs(mpg123_handle *fr, off_t ins) 105 { 106 off_t soff = 0; 107 off_t ntm = ntom_val(fr,0); 108 #ifdef SAFE_NTOM 109 { 110 off_t block = fr->spf; 111 if(ins <= 0) return 0; 112 do 113 { 114 off_t nowblock = ins > block ? block : ins; 115 ntm += nowblock*fr->ntom_step; 116 soff += ntm/NTOM_MUL; 117 ntm -= (ntm/NTOM_MUL)*NTOM_MUL; 118 ins -= nowblock; 119 } while(ins > 0); 120 } 121 #else 122 /* Beware of overflows: when off_t is 32bits, the multiplication blows too easily. 123 Of course, it blows for 64bits, too, in theory, but that's for _really_ large files. */ 124 soff = ((off_t)ntm + (off_t)ins*(off_t)fr->ntom_step)/(off_t)NTOM_MUL; 125 #endif 126 return soff; 127 } 128 129 /* Determine frame offset from unadjusted output sample offset. */ 130 off_t ntom_frameoff(mpg123_handle *fr, off_t soff) 131 { 132 off_t ioff = 0; /* frames or samples */ 133 off_t ntm = ntom_val(fr,0); 134 #ifdef SAFE_NTOM 135 if(soff <= 0) return 0; 136 for(ioff=0; 1; ++ioff) 137 { 138 ntm += fr->spf*fr->ntom_step; 139 if(ntm/NTOM_MUL > soff) break; 140 soff -= ntm/NTOM_MUL; 141 ntm -= (ntm/NTOM_MUL)*NTOM_MUL; 142 } 143 return ioff; 144 #else 145 ioff = (soff*(off_t)NTOM_MUL-ntm)/(off_t)fr->ntom_step; 146 return ioff/(off_t)fr->spf; 147 #endif 148 } 149