file/magic/scripts/create_filemagic_flac

#!/usr/bin/env bash

## bash script to generate file magic support for flac.
## https://github.com/file/file/blob/master/magic/Magdir/audio
## below "#some common sample rates" (line 471), ie:
## >>17	belong&0xfffff0		0x2ee000	\b, 192 kHz

LANG=C

target=magic/Magdir/audio

## construct static list of sample rates based on standard crystal
## oscillator frequencies.
## 16.384  MHz Unknown audio application
##             (16384 kHz  = 32 kHz * 512 = 32 * 2^9)
## 22.5792 MHz Redbook/CD
##             (22579.2 kHz = 44.1kHz * 512 = 44.1 * 2^9)
##             also used: 11.2896, 16.9344, 33.8688 and 45.1584
## 24.576  MHz DAT/Video
##             (24576 kHz = 48 kHz * 512 = 48 * 2^9)
##             also used: 49.1520

## 33.8688 > 16.9344
## 36.864  > 18.432000
declare -a a_ground_fs=(16384000 22579200 24576000)

## multiply ground clock frequencies by 1953 to get usable base
## frequencies, for instance:
##  DAT/video:  24.576  MHz * 1000000 / 512 = 48000Hz
##  Redbook/CD: 22.5792 MHz * 1000000 / 512 = 44100Hz
## use base rates for calculating derived rates
declare -a samplerates
## min divider: fs/n
def_fs_n=512
min_fs_n=4
## start at base_fs/(def_fs*min_fs)
## add each derived sample rate to the array
for base_fs in "${a_ground_fs[@]}"; do 
    min_fs=$( echo "${base_fs} / ( ${def_fs_n} * ${min_fs_n} )" | bc)
    ## max multiplier: fs*n*min_fs
    max_fs_n=$(( 8 * min_fs_n ))
    n=${max_fs_n}
    while [[ ${n} -ge 1 ]]; do
	sample_rate=$(( min_fs * n ))
	samplerates+=(${sample_rate})
	n=$(( n / 2 ))
    done
done

declare -a stripped_rates
declare -a lines
for samplerate in "${samplerates[@]}"; do
    ## use bc with sed to convert and format Hz to kHz
    stripped_rate="$(LANG=C bc <<< "scale=5; ${samplerate} / 1000" | \
			      sed 's#[0\.]*$##g')"
    ## only add uniq sample rates (should be necessary
    if [[ ! "${stripped_rates[@]}" =~ ${stripped_rate} ]]; then
	printf -v line ">>17\tbelong&%#-15x\t%#08x\t%s, %s kHz\n" \
	       "16777200" \
	       "$(( samplerate * 16 ))" \
	       "\b" \
	       "${stripped_rate}"
	stripped_rates+=("${stripped_rate}")
	lines+=("${line}")
    fi

done
printf "## start cutting >>> \n"
## print out the formatted lines
printf "%s" "${lines[@]}" | sort -k5 -n
printf "## <<< stop cutting\n"