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peakmeter: Make a smaller, cleaner calc_db().

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Use a binary tree in an array.

Change-Id: I392d71fddae21e900ff9e97deed54e0a843e4eb9
This commit is contained in:
Michael Sevakis 2017-12-11 16:44:24 -05:00
parent 80a0bf590f
commit c53c617976
1 changed files with 55 additions and 73 deletions
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128
apps/recorder/peakmeter.c
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@ -194,93 +194,75 @@ static int db_scale_count = DB_SCALE_SRC_VALUES_SIZE;
* The calculation is based on the results of a linear
* approximation tool written specifically for this problem
* by Andreas Zwirtes (radhard@gmx.de). The result has an
* accurracy of better than 2%. It is highly runtime optimized,
* the cascading if-clauses do an successive approximation on
* the input value. This avoids big lookup-tables and
* for-loops.
* accurracy of better than 2%.
*
* The search tree does a binary search on the input value.
*
* Marked "NO_INLINE" because GCC really wants to inline it
* in some cases.
*.
* Improved by Jvo Studer for errors < 0.2dB for critical
* range of -12dB to 0dB (78.0 to 90.0dB).
*/
static int calc_db (int isample)
static NO_INLINE int calc_db (int isample)
{
/* return n+m*(isample-istart)/100 */
int n;
long m;
int istart;
/* Search tree:
*
* ________2308_______
* ___115___ _12932_
* __24__ __534__ _6394_ _22450_
* _5_ d0 d1 d2 d3 d4 d5 d6
* d7 d8
*/
static const int16_t keys[] =
{
0, /* 1-based array */
2308,
115,
12932,
24,
534,
6394,
22450,
5,
};
if (isample < 2308) { /* Range 1-5 */
/* To ensure no overflow in the computations throughout the operational
range, M_FRAC_BITS must be 20 or less. The full range of isample for
20 fractional bits without overflowing int32_t is [-4, 90903]. */
#define M_FRAC_BITS 20
#define M_FIXED(m) ((int32_t)(((int64_t)(m) << M_FRAC_BITS) / 100))
if (isample < 115) { /* Range 1-3 */
static const struct {
int16_t istart;
int16_t n;
int32_t m;
} data[] =
{
{ .istart = 24, .n = 2858, .m = M_FIXED( 1498) },
{ .istart = 114, .n = 4207, .m = M_FIXED( 319) },
{ .istart = 588, .n = 5583, .m = M_FIXED( 69) },
{ .istart = 2608, .n = 6832, .m = M_FIXED( 21) },
{ .istart = 7000, .n = 7682, .m = M_FIXED( 9) },
{ .istart = 13000, .n = 8219, .m = M_FIXED( 5) },
{ .istart = 22636, .n = 8697, .m = M_FIXED( 3) },
{ .istart = 1, .n = 98, .m = M_FIXED(34950) },
{ .istart = 5, .n = 1496, .m = M_FIXED( 7168) },
};
if (isample < 24) {
int i = 1;
if (isample < 5) {
istart = 1; /* Range 1 */
n = 98;
m = 34950;
}
else {
istart = 5; /* Range 2 */
n = 1496;
m = 7168;
}
}
else {
istart = 24; /* Range 3 */
n = 2858;
m = 1498;
}
}
else { /* Range 4-5 */
if (isample < 534) {
istart = 114; /* Range 4 */
n = 4207;
m = 319;
}
else {
istart = 588; /* Range 5 */
n = 5583;
m = 69;
}
}
/* Runs 3 times if isample >= 24, else 4 */
while (i < 9) {
i = 2*i + (isample >= keys[i]);
}
else { /* Range 6-9 */
i -= 9;
if (isample < 12932) {
if (isample < 6394) {
istart = 2608; /* Range 6 */
n = 6832;
m = 21;
}
else {
istart = 7000; /* Range 7 */
n = 7682;
m = 9;
}
}
else {
if (isample < 22450) {
istart = 13000; /* Range 8 */
n = 8219;
m = 5;
}
else {
istart = 22636; /* Range 9 */
n = 8697;
m = 3;
}
}
}
return n + (m * (long)(isample - istart)) / 100L;
return data[i].n + (data[i].m * (isample - data[i].istart) >> M_FRAC_BITS);
}
/**
* A helper function for peak_meter_db2sample. Don't call it separately but
* use peak_meter_db2sample. If one or both of min and max are outside the