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| author | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2018-06-05 16:15:27 +0100 |
|---|---|---|
| committer | Szabolcs Nagy <szabolcs.nagy@arm.com> | 2018-06-06 16:17:19 +0100 |
| commit | d69e504577169c5f75803f1b97a42822898a78b3 (patch) | |
| tree | 6196f61c3386e50ad8257d6a1f21c90ef39dddb8 /math/math_config.h | |
| parent | a7711a35d57cae0c9fcf0cd61903bbf4701240cf (diff) | |
| download | arm-optimized-routines-d69e504577169c5f75803f1b97a42822898a78b3.tar.gz | |
Add new log2 implementation
Similar algorithm is used as in log, but there are more operations
(and more error) due to the 1/ln2 multiplier.
There is separate code path when fma instruction is not available for
computing x/c - 1 precisely, for which the table size is doubled,
and to compute (x/c - 1)/ln2 precisely.
The worst case error is 0.547 ULP (0.55 without fma), the read only
global data size is 1168 bytes (2192 without fma). The non-nearest
rounding error is less than 1 ULP.
Improvements on Cortex-A72 compared to current glibc master:
log latency: 2.04x
log thruput: 1.87x
Diffstat (limited to 'math/math_config.h')
| -rw-r--r-- | math/math_config.h | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/math/math_config.h b/math/math_config.h index 3383e70..28b7d26 100644 --- a/math/math_config.h +++ b/math/math_config.h @@ -309,4 +309,18 @@ extern const struct log_data { #endif } __log_data HIDDEN; +#define LOG2_TABLE_BITS 6 +#define LOG2_POLY_ORDER 7 +#define LOG2_POLY1_ORDER 11 +extern const struct log2_data { + double invln2hi; + double invln2lo; + double poly[LOG2_POLY_ORDER - 1]; + double poly1[LOG2_POLY1_ORDER - 1]; + struct {double invc, logc;} tab[1 << LOG2_TABLE_BITS]; +#if !HAVE_FAST_FMA + struct {double chi, clo;} tab2[1 << LOG2_TABLE_BITS]; +#endif +} __log2_data HIDDEN; + #endif |