From fbf649146abc525610b0370453df01b227712b29 Mon Sep 17 00:00:00 2001
From: Richard Fuchs <rfuchs@sipwise.com>
Date: Tue, 5 Oct 2021 12:42:21 -0400
Subject: [PATCH] TT#136956 convert pow() usage to lookup table

Change-Id: If16607fb1f6cf14e0cc3dbc7bd288291325d8473
---
 lib/dtmflib.c | 147 ++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 143 insertions(+), 4 deletions(-)

diff --git a/lib/dtmflib.c b/lib/dtmflib.c
index a2c6da269..4b3e91065 100644
--- a/lib/dtmflib.c
+++ b/lib/dtmflib.c
@@ -35,6 +35,138 @@ INLINE double freq2iter(unsigned int hz, unsigned int sample_rate) {
 	return ret;
 }
 
+// pow(1.122018, x)
+static const double vol_table[] = {
+	1.0,
+	1.122018,
+	1.2589243923239999,
+	1.4125358288265897,
+	1.5848906255883524,
+	1.778275809941392,
+	1.9952574677188206,
+	2.238714793414936,
+	2.5118782950778393,
+	2.818372660886647,
+	3.1622648562227136,
+	3.5481180894492965,
+	3.9810523624877208,
+	4.466812409653747,
+	5.011843926254878,
+	5.623379098448646,
+	6.309532569283152,
+	7.079409114321943,
+	7.9432244556332785,
+	8.91244081726074,
+	9.99991902090126,
+	11.22008913999359,
+	12.589141976677327,
+	14.12524390238754,
+	15.848777912869062,
+	17.78261409624152,
+	19.952413103036715,
+	22.38696664504305,
+	25.118579541137912,
+	28.183498379588475,
+	31.6223924848691,
+	35.480893571087854,
+	39.810201242844855,
+	44.667762378094295,
+	50.1180334079446,
+	56.23333560831519,
+	63.094814752570585,
+	70.79351785904974,
+	79.43160132117526,
+	89.12368645118244,
+	99.9983804245828,
+	112.19998280722955,
+	125.89040030940208,
+	141.25129517435468,
+	158.4864957089391,
+	177.82470094235242,
+	199.52251530193638,
+	223.86785357404804,
+	251.18376133144622,
+	281.8327015215866,
+	316.22136409584755,
+	354.8060625000947,
+	398.0987886342312,
+	446.6740066258028,
+	501.17627556627,
+	562.3288023583151,
+	630.943038164472,
+	707.9294457952245,
+	794.3095809122663,
+	891.2296473560191,
+	999.9757064671057,
+	1121.9907422188091,
+	1258.8938086028636,
+	1412.501513340968,
+	1584.852122995806,
+	1778.2326093395081,
+	1995.2089958658962,
+	2238.660407123461,
+	2511.8172726798516,
+	2818.3041926577016,
+	3162.188033637409,
+	3548.031893125778,
+	3980.955648661199,
+	4466.703894999541,
+	5011.722170859594,
+	5623.242486703541,
+	6309.379288446133,
+	7079.237130463753,
+	7943.031486648679,
+	8912.224302586577,
+	9999.676087539585,
+	11219.81656438899,
+	12588.836141942606,
+	14124.900750310158,
+	15848.392890061503,
+	17782.182093721025,
+	19951.928388432676,
+	22386.422786532454,
+	25117.969322099572,
+	28182.813702843516,
+	31621.624265237075,
+	35480.03161483277,
+	39809.23411241143,
+	44666.67724033965,
+	50116.815863851414,
+	56231.96950192683,
+	63093.28195661294,
+	70791.79803439493,
+	79429.67164695573,
+	89121.52132197398,
+	99995.95111063859,
+	112197.2570732565,
+	125887.34198682109,
+	141247.86368136902,
+	158482.6455120423,
+	177820.38095213068,
+	199517.66819514774,
+	223862.4150329833,
+	251177.65919047783,
+	281825.85480958153,
+	316213.68196173705,
+	354797.44300734426,
+	398089.11740821437,
+	446663.1553361299,
+	501164.10022393375,
+	562315.1414050576,
+	630927.7103290199,
+	707912.2476879463,
+	794290.2843263341,
+	891207.9962392647,
+	999951.4135243873,
+	1121963.485099806,
+	1258863.225624714,
+	1412467.1986889902,
+	1584813.6213386236,
+	1778189.4097871196,
+	1995160.5251905243,
+	2238606.0221532215,
+};
+
 // only packed audio supported
 
 #define freq_samples_x(type, mult) \
@@ -43,12 +175,19 @@ INLINE void freq_samples_ ## type(type *samples, unsigned long offset, unsigned
 { \
 	if (!channels) \
 		channels = 1; \
-	/* XXX initialise/save these when the DTMF event starts */ \
-	double vol = pow(1.122018, volume) * 2.0; \
- \
+\
+	double vol; \
+	if (volume < G_N_ELEMENTS(vol_table)) \
+		vol = vol_table[volume]; \
+	else \
+		vol = pow(1.122018, volume); \
+\
+	if (sec_freq) /* halve volume of we have two tones */ \
+		vol *= 2.0; \
+\
 	double prim_iter = freq2iter(prim_freq, sample_rate); \
 	double sec_iter = sec_freq ? freq2iter(sec_freq, sample_rate) : 0; \
- \
+\
 	num += offset; /* end here */ \
 	while (offset < num) { \
 		double prim = sin(prim_iter * offset) / vol; \