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| author | Nicholas Dingle <Nicholas.Dingle@arm.com> | 2022-11-15 14:55:06 +0000 |
|---|---|---|
| committer | Joe Ramsay <joe.ramsay@arm.com> | 2022-11-15 14:55:06 +0000 |
| commit | c1cf1eb0ad5fb98c4c14e8e83e00b779d1e646a2 (patch) | |
| tree | 7ba2bb2e9937fc95cfed4175333b5456cf2a206f /pl/math/v_log2_3u.c | |
| parent | 3560d66f2efb0164821681e5006280b2f6dadd07 (diff) | |
| download | arm-optimized-routines-c1cf1eb0ad5fb98c4c14e8e83e00b779d1e646a2.tar.gz | |
pl/math: Use order-6 polynomial in Vector/Neon log2
Reduce the order of the polynomial used in Neon log2 by one (from 7 to
6). In order to calculate the new coefficients required we rescale the
coefficients from log_data.c by log2(e) in extended precision and
round back.
The maximum observed error is unchanged (2.59 ULPs) but the point at
which it is observed has changed slightly.
Diffstat (limited to 'pl/math/v_log2_3u.c')
| -rw-r--r-- | pl/math/v_log2_3u.c | 7 |
1 files changed, 3 insertions, 4 deletions
diff --git a/pl/math/v_log2_3u.c b/pl/math/v_log2_3u.c index b076874..af7340d 100644 --- a/pl/math/v_log2_3u.c +++ b/pl/math/v_log2_3u.c @@ -46,8 +46,8 @@ specialcase (v_f64_t x, v_f64_t y, v_u64_t cmp) /* Double-precision vector log2 routine. Implements the same algorithm as vector log10, with coefficients and table entries scaled in extended precision. The maximum observed error is 2.59 ULP: - __v_log2(0x1.0b556e53a80b6p+0) got 0x1.fffbc594d146bp-5 - want 0x1.fffbc594d146ep-5. */ + __v_log2(0x1.0b555054a9bd1p+0) got 0x1.fff6977bdced3p-5 + want 0x1.fff6977bdced6p-5. */ VPCS_ATTR v_f64_t V_NAME (log2) (v_f64_t x) { @@ -73,10 +73,9 @@ v_f64_t V_NAME (log2) (v_f64_t x) v_f64_t w = v_fma_f64 (r, InvLn2, e.log2c); v_f64_t r2 = r * r; - v_f64_t p_45 = v_fma_f64 (P (5), r, P (4)); v_f64_t p_23 = v_fma_f64 (P (3), r, P (2)); v_f64_t p_01 = v_fma_f64 (P (1), r, P (0)); - v_f64_t y = v_fma_f64 (r2, p_45, p_23); + v_f64_t y = v_fma_f64 (P (4), r2, p_23); y = v_fma_f64 (r2, y, p_01); y = v_fma_f64 (r2, y, kd + w); |