diff mbox

[RFC,v2,1/2] Btrfs: add precomputed log2()

Message ID 20170626012456.19872-2-nefelim4ag@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Timofey Titovets June 26, 2017, 1:24 a.m. UTC 
Heuristic code compute shannon entropy in cases when
other methods can't make clear decision
For realization that calculation it's needs floating point,
but as this doesn't possible to use floating point,
lets just precalculate all our input/output values

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
---
 fs/btrfs/log2_lshift16.c | 278 +++++++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/log2_lshift16.h |  11 ++
 2 files changed, 289 insertions(+)
 create mode 100644 fs/btrfs/log2_lshift16.c
 create mode 100644 fs/btrfs/log2_lshift16.h

--
2.13.1
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diff mbox

Patch

diff --git a/fs/btrfs/log2_lshift16.c b/fs/btrfs/log2_lshift16.c
new file mode 100644
index 000000000000..0d5d414b2adf
--- /dev/null
+++ b/fs/btrfs/log2_lshift16.c
@@ -0,0 +1,278 @@ 
+#include <linux/types.h>
+#include "log2_lshift16.h"
+
+/*
+ * Precalculated log2 values
+ * Shifting used for avoiding floating point
+ * Fraction must be left shifted by 16
+ * Return of log are left shifted by 3
+ */
+int log2_lshift16(u64 lshift16)
+{
+	if (lshift16 < 558) {
+		if (lshift16 < 54) {
+			if (lshift16 < 13) {
+				if (lshift16 < 7) {
+					if (lshift16 < 1)
+						return -136;
+					if (lshift16 < 2)
+						return -123;
+					if (lshift16 < 3)
+						return -117;
+					if (lshift16 < 4)
+						return -113;
+					if (lshift16 < 5)
+						return -110;
+					if (lshift16 < 6)
+						return -108;
+					if (lshift16 < 7)
+						return -106;
+				} else {
+					if (lshift16 < 8)
+						return -104;
+					if (lshift16 < 9)
+						return -103;
+					if (lshift16 < 10)
+						return -102;
+					if (lshift16 < 11)
+						return -100;
+					if (lshift16 < 12)
+						return -99;
+					if (lshift16 < 13)
+						return -98;
+				}
+			} else {
+				if (lshift16 < 29) {
+					if (lshift16 < 15)
+						return -97;
+					if (lshift16 < 16)
+						return -96;
+					if (lshift16 < 17)
+						return -95;
+					if (lshift16 < 19)
+						return -94;
+					if (lshift16 < 21)
+						return -93;
+					if (lshift16 < 23)
+						return -92;
+					if (lshift16 < 25)
+						return -91;
+					if (lshift16 < 27)
+						return -90;
+					if (lshift16 < 29)
+						return -89;
+				} else {
+					if (lshift16 < 32)
+						return -88;
+					if (lshift16 < 35)
+						return -87;
+					if (lshift16 < 38)
+						return -86;
+					if (lshift16 < 41)
+						return -85;
+					if (lshift16 < 45)
+						return -84;
+					if (lshift16 < 49)
+						return -83;
+					if (lshift16 < 54)
+						return -82;
+				}
+			}
+		} else {
+			if (lshift16 < 181) {
+				if (lshift16 < 99) {
+					if (lshift16 < 59)
+						return -81;
+					if (lshift16 < 64)
+						return -80;
+					if (lshift16 < 70)
+						return -79;
+					if (lshift16 < 76)
+						return -78;
+					if (lshift16 < 83)
+						return -77;
+					if (lshift16 < 91)
+						return -76;
+					if (lshift16 < 99)
+						return -75;
+				} else {
+					if (lshift16 < 108)
+						return -74;
+					if (lshift16 < 117)
+						return -73;
+					if (lshift16 < 128)
+						return -72;
+					if (lshift16 < 140)
+						return -71;
+					if (lshift16 < 152)
+						return -70;
+					if (lshift16 < 166)
+						return -69;
+					if (lshift16 < 181)
+						return -68;
+				}
+			} else {
+				if (lshift16 < 304) {
+					if (lshift16 < 197)
+						return -67;
+					if (lshift16 < 215)
+						return -66;
+					if (lshift16 < 235)
+						return -65;
+					if (lshift16 < 256)
+						return -64;
+					if (lshift16 < 279)
+						return -63;
+					if (lshift16 < 304)
+						return -62;
+				} else {
+					if (lshift16 < 332)
+						return -61;
+					if (lshift16 < 362)
+						return -60;
+					if (lshift16 < 395)
+						return -59;
+					if (lshift16 < 431)
+						return -58;
+					if (lshift16 < 470)
+						return -57;
+					if (lshift16 < 512)
+						return -56;
+					if (lshift16 < 558)
+						return -55;
+				}
+			}
+		}
+	} else {
+		if (lshift16 < 6317) {
+			if (lshift16 < 2048) {
+				if (lshift16 < 1117) {
+					if (lshift16 < 609)
+						return -54;
+					if (lshift16 < 664)
+						return -53;
+					if (lshift16 < 724)
+						return -52;
+					if (lshift16 < 790)
+						return -51;
+					if (lshift16 < 861)
+						return -50;
+					if (lshift16 < 939)
+						return -49;
+					if (lshift16 < 1024)
+						return -48;
+					if (lshift16 < 1117)
+						return -47;
+				} else {
+					if (lshift16 < 1218)
+						return -46;
+					if (lshift16 < 1328)
+						return -45;
+					if (lshift16 < 1448)
+						return -44;
+					if (lshift16 < 1579)
+						return -43;
+					if (lshift16 < 1722)
+						return -42;
+					if (lshift16 < 1878)
+						return -41;
+					if (lshift16 < 2048)
+						return -40;
+				}
+			} else {
+				if (lshift16 < 3756) {
+					if (lshift16 < 2233)
+						return -39;
+					if (lshift16 < 2435)
+						return -38;
+					if (lshift16 < 2656)
+						return -37;
+					if (lshift16 < 2896)
+						return -36;
+					if (lshift16 < 3158)
+						return -35;
+					if (lshift16 < 3444)
+						return -34;
+					if (lshift16 < 3756)
+						return -33;
+				} else {
+					if (lshift16 < 4096)
+						return -32;
+					if (lshift16 < 4467)
+						return -31;
+					if (lshift16 < 4871)
+						return -30;
+					if (lshift16 < 5312)
+						return -29;
+					if (lshift16 < 5793)
+						return -28;
+					if (lshift16 < 6317)
+						return -27;
+				}
+			}
+		} else {
+			if (lshift16 < 21247) {
+				if (lshift16 < 11585) {
+					if (lshift16 < 6889)
+						return -26;
+					if (lshift16 < 7512)
+						return -25;
+					if (lshift16 < 8192)
+						return -24;
+					if (lshift16 < 8933)
+						return -23;
+					if (lshift16 < 9742)
+						return -22;
+					if (lshift16 < 10624)
+						return -21;
+					if (lshift16 < 11585)
+						return -20;
+				} else {
+					if (lshift16 < 12634)
+						return -19;
+					if (lshift16 < 13777)
+						return -18;
+					if (lshift16 < 15024)
+						return -17;
+					if (lshift16 < 16384)
+						return -16;
+					if (lshift16 < 17867)
+						return -15;
+					if (lshift16 < 19484)
+						return -14;
+					if (lshift16 < 21247)
+						return -13;
+				}
+			} else {
+				if (lshift16 < 35734) {
+					if (lshift16 < 23170)
+						return -12;
+					if (lshift16 < 25268)
+						return -11;
+					if (lshift16 < 27554)
+						return -10;
+					if (lshift16 < 30048)
+						return -9;
+					if (lshift16 < 32768)
+						return -8;
+					if (lshift16 < 35734)
+						return -7;
+				} else {
+					if (lshift16 < 38968)
+						return -6;
+					if (lshift16 < 42495)
+						return -5;
+					if (lshift16 < 46341)
+						return -4;
+					if (lshift16 < 50535)
+						return -3;
+					if (lshift16 < 55109)
+						return -2;
+					if (lshift16 < 60097)
+						return -1;
+				}
+			}
+		}
+	}
+	return 0;
+}
diff --git a/fs/btrfs/log2_lshift16.h b/fs/btrfs/log2_lshift16.h
new file mode 100644
index 000000000000..fba434e3984a
--- /dev/null
+++ b/fs/btrfs/log2_lshift16.h
@@ -0,0 +1,11 @@ 
+#include <linux/types.h>
+/*
+ * Precalculated log2 values
+ * Shifting used for avoiding floating point
+ * Fraction must be left shifted by 16
+ * Return of log are left shifted by 3
+ */
+
+#define LOG2_ARG_SHIFT (1 << 16)
+#define LOG2_RET_SHIFT (1 << 3)
+int log2_lshift16(u64 lshift16);