[PATCH 5/8] math: Sync log with Arm Optimized Routines
Adhemerval Zanella
adhemerval.zanella@linaro.org
Thu Feb 26 20:01:51 GMT 2026
Sync with commit 712aa21 for log.c and 189dfef for log_data.c.
No functional change.
Checked on x86_64-linux-gnu, i686-linux-gnu, and aarch64-linux-gnu.
---
sysdeps/ieee754/dbl-64/e_log.c | 49 ++++++-
sysdeps/ieee754/dbl-64/e_log_data.c | 183 ++++++++++++++++++++++++++-
sysdeps/ieee754/dbl-64/math_config.h | 3 +-
3 files changed, 225 insertions(+), 10 deletions(-)
diff --git a/sysdeps/ieee754/dbl-64/e_log.c b/sysdeps/ieee754/dbl-64/e_log.c
index d8abde10aa..9f9b82f05f 100644
--- a/sysdeps/ieee754/dbl-64/e_log.c
+++ b/sysdeps/ieee754/dbl-64/e_log.c
@@ -55,8 +55,13 @@ __log (double x)
ix = asuint64 (x);
top = top16 (x);
-#define LO asuint64 (1.0 - 0x1p-4)
-#define HI asuint64 (1.0 + 0x1.09p-4)
+#if LOG_POLY1_ORDER == 10 || LOG_POLY1_ORDER == 11
+# define LO asuint64 (1.0 - 0x1p-5)
+# define HI asuint64 (1.0 + 0x1.1p-5)
+#elif LOG_POLY1_ORDER == 12
+# define LO asuint64 (1.0 - 0x1p-4)
+# define HI asuint64 (1.0 + 0x1.09p-4)
+#endif
if (__glibc_unlikely (ix - LO < HI - LO))
{
/* Handle close to 1.0 inputs separately. */
@@ -66,9 +71,34 @@ __log (double x)
r = x - 1.0;
r2 = r * r;
r3 = r * r2;
+#if LOG_POLY1_ORDER == 10
+ /* Worst-case error is around 0.516 ULP. */
+ y = r3 * (B[1] + r * B[2] + r2 * B[3]
+ + r3 * (B[4] + r * B[5] + r2 * B[6] + r3 * (B[7] + r * B[8])));
+ w = B[0] * r2; /* B[0] == -0.5. */
+ hi = r + w;
+ y += r - hi + w;
+ y += hi;
+#elif LOG_POLY1_ORDER == 11
+ /* Worst-case error is around 0.516 ULP. */
+ y = r3 * (B[1] + r * B[2]
+ + r2 * (B[3] + r * B[4] + r2 * B[5]
+ + r3 * (B[6] + r * B[7] + r2 * B[8] + r3 * B[9])));
+ w = B[0] * r2; /* B[0] == -0.5. */
+ hi = r + w;
+ y += r - hi + w;
+ y += hi;
+#elif LOG_POLY1_ORDER == 12
y = r3 * (B[1] + r * B[2] + r2 * B[3]
+ r3 * (B[4] + r * B[5] + r2 * B[6]
+ r3 * (B[7] + r * B[8] + r2 * B[9] + r3 * B[10])));
+# if N <= 64
+ /* Worst-case error is around 0.532 ULP. */
+ w = B[0] * r2; /* B[0] == -0.5. */
+ hi = r + w;
+ y += r - hi + w;
+ y += hi;
+# else
/* Worst-case error is around 0.507 ULP. */
w = r * 0x1p27;
double rhi = r + w - w;
@@ -79,6 +109,8 @@ __log (double x)
lo += B[0] * rlo * (rhi + r);
y += lo;
y += hi;
+# endif
+#endif
return y;
}
if (__glibc_unlikely (top - 0x0010 >= 0x7ff0 - 0x0010))
@@ -110,7 +142,7 @@ __log (double x)
/* r ~= z/c - 1, |r| < 1/(2*N). */
#ifdef __FP_FAST_FMA
/* rounding error: 0x1p-55/N. */
- r = __builtin_fma (z, invc, -1.0);
+ r = fma (z, invc, -1.0);
#else
/* rounding error: 0x1p-55/N + 0x1p-66. */
r = (z - T2[i].chi - T2[i].clo) * invc;
@@ -124,9 +156,18 @@ __log (double x)
/* log(x) = lo + (log1p(r) - r) + hi. */
r2 = r * r; /* rounding error: 0x1p-54/N^2. */
- /* Worst case error if |y| > 0x1p-4: 0.519 ULP (0.520 ULP without fma).
+ /* Worst case error if |y| > 0x1p-5:
+ 0.5 + 4.13/N + abs-poly-error*2^57 ULP (+ 0.002 ULP without fma)
+ Worst case error if |y| > 0x1p-4:
0.5 + 2.06/N + abs-poly-error*2^56 ULP (+ 0.001 ULP without fma). */
+#if LOG_POLY_ORDER == 6
y = lo + r2 * A[0] + r * r2 * (A[1] + r * A[2] + r2 * (A[3] + r * A[4])) + hi;
+#elif LOG_POLY_ORDER == 7
+ y = lo
+ + r2 * (A[0] + r * A[1] + r2 * (A[2] + r * A[3])
+ + r2 * r2 * (A[4] + r * A[5]))
+ + hi;
+#endif
return y;
}
#ifndef __log
diff --git a/sysdeps/ieee754/dbl-64/e_log_data.c b/sysdeps/ieee754/dbl-64/e_log_data.c
index c3b862ba6f..460fd6a488 100644
--- a/sysdeps/ieee754/dbl-64/e_log_data.c
+++ b/sysdeps/ieee754/dbl-64/e_log_data.c
@@ -24,7 +24,32 @@ const struct log_data __log_data = {
.ln2hi = 0x1.62e42fefa3800p-1,
.ln2lo = 0x1.ef35793c76730p-45,
.poly1 = {
-#if LOG_POLY1_ORDER == 12
+#if LOG_POLY1_ORDER == 10
+// relative error: 0x1.32eccc6p-62
+// in -0x1p-5 0x1.1p-5 (|log(1+x)| > 0x1p-5 outside this interval)
+-0x1p-1,
+0x1.55555555554e5p-2,
+-0x1.0000000000af2p-2,
+0x1.9999999bbe436p-3,
+-0x1.55555537f9cdep-3,
+0x1.24922fc8127cfp-3,
+-0x1.0000b7d6bb612p-3,
+0x1.c806ee1ddbcafp-4,
+-0x1.972335a9c2d6ep-4,
+#elif LOG_POLY1_ORDER == 11
+// relative error: 0x1.52c8b708p-68
+// in -0x1p-5 0x1.1p-5 (|log(1+x)| > 0x1p-5 outside this interval)
+-0x1p-1,
+0x1.5555555555555p-2,
+-0x1.ffffffffffea9p-3,
+0x1.999999999c4d4p-3,
+-0x1.55555557f5541p-3,
+0x1.249248fbe33e4p-3,
+-0x1.ffffc9a3c825bp-4,
+0x1.c71e1f204435dp-4,
+-0x1.9a7f26377d06ep-4,
+0x1.71c30cf8f7364p-4,
+#elif LOG_POLY1_ORDER == 12
// relative error: 0x1.c04d76cp-63
// in -0x1p-4 0x1.09p-4 (|log(1+x)| > 0x1p-4 outside the interval)
-0x1p-1,
@@ -41,7 +66,17 @@ const struct log_data __log_data = {
#endif
},
.poly = {
-#if N == 128 && LOG_POLY_ORDER == 6
+#if N == 64 && LOG_POLY_ORDER == 7
+// relative error: 0x1.906eb8ap-58
+// abs error: 0x1.d2cad5a8p-67
+// in -0x1.fp-8 0x1.fp-8
+-0x1.0000000000027p-1,
+0x1.555555555556ap-2,
+-0x1.fffffff0440bap-3,
+0x1.99999991906c3p-3,
+-0x1.555c8d7e8201ep-3,
+0x1.24978c59151fap-3,
+#elif N == 128 && LOG_POLY_ORDER == 6
// relative error: 0x1.926199e8p-56
// abs error: 0x1.882ff33p-65
// in -0x1.fp-9 0x1.fp-9
@@ -50,6 +85,16 @@ const struct log_data __log_data = {
-0x1.fffffffeb459p-3,
0x1.999b324f10111p-3,
-0x1.55575e506c89fp-3,
+#elif N == 128 && LOG_POLY_ORDER == 7
+// relative error: 0x1.649fc4bp-64
+// abs error: 0x1.c3b5769p-74
+// in -0x1.fp-9 0x1.fp-9
+-0x1.0000000000001p-1,
+0x1.5555555555556p-2,
+-0x1.fffffffea1a8p-3,
+0x1.99999998e9139p-3,
+-0x1.555776801b968p-3,
+0x1.2493c29331a5cp-3,
#endif
},
/* Algorithm:
@@ -79,7 +124,72 @@ a single rounding error when there is no fast fma for z*invc - 1, 3) ensures
that logc + poly(z/c - 1) has small error, however near x == 1 when
|log(x)| < 0x1p-4, this is not enough so that is special cased. */
.tab = {
-#if N == 128
+#if N == 64
+{0x1.7242886495cd8p+0, -0x1.79e267bdfe000p-2},
+{0x1.6e1f769340dc9p+0, -0x1.6e60ee0ecb000p-2},
+{0x1.6a13ccc8f195cp+0, -0x1.63002fdbf6000p-2},
+{0x1.661ec72e86f3ap+0, -0x1.57bf76c597000p-2},
+{0x1.623fa6c447b16p+0, -0x1.4c9e07f0d2000p-2},
+{0x1.5e75bbca31702p+0, -0x1.419b42f027000p-2},
+{0x1.5ac05655adb10p+0, -0x1.36b67660e6000p-2},
+{0x1.571ed3e940191p+0, -0x1.2bef0839e4800p-2},
+{0x1.539094ac0fbbfp+0, -0x1.21445727cb000p-2},
+{0x1.5015007e7fc42p+0, -0x1.16b5ca3c3d000p-2},
+{0x1.4cab877c31cf9p+0, -0x1.0c42d3805f800p-2},
+{0x1.49539e76a88d3p+0, -0x1.01eae61b60800p-2},
+{0x1.460cbc12211dap+0, -0x1.ef5adb9fb0000p-3},
+{0x1.42d6624debe3ap+0, -0x1.db13daab99000p-3},
+{0x1.3fb0144f0d462p+0, -0x1.c6ffbe896e000p-3},
+{0x1.3c995a1f9a9b4p+0, -0x1.b31d84722d000p-3},
+{0x1.3991c23952500p+0, -0x1.9f6c3cf6eb000p-3},
+{0x1.3698df35eaa14p+0, -0x1.8beafe7f13000p-3},
+{0x1.33ae463091760p+0, -0x1.7898db878d000p-3},
+{0x1.30d190aae3d72p+0, -0x1.6574efe4ec000p-3},
+{0x1.2e025c9203c89p+0, -0x1.527e620845000p-3},
+{0x1.2b404a7244988p+0, -0x1.3fb457d798000p-3},
+{0x1.288b01dc19544p+0, -0x1.2d1615a077000p-3},
+{0x1.25e2268085f69p+0, -0x1.1aa2b431e5000p-3},
+{0x1.23456812abb74p+0, -0x1.08598f1d2b000p-3},
+{0x1.20b4703174157p+0, -0x1.ec738fee40000p-4},
+{0x1.1e2ef308b4e9bp+0, -0x1.c885768862000p-4},
+{0x1.1bb4a36b70a3fp+0, -0x1.a4e75b6a46000p-4},
+{0x1.194538e960658p+0, -0x1.8197efba9a000p-4},
+{0x1.16e0692a10ac8p+0, -0x1.5e95ad734e000p-4},
+{0x1.1485f1ba1568bp+0, -0x1.3bdf67117c000p-4},
+{0x1.12358e123ed6fp+0, -0x1.1973b744f0000p-4},
+{0x1.0fef01de37c8dp+0, -0x1.eea33446bc000p-5},
+{0x1.0db20b82be414p+0, -0x1.aaef4ab304000p-5},
+{0x1.0b7e6f67f69b3p+0, -0x1.67c962fd2c000p-5},
+{0x1.0953f342fc108p+0, -0x1.252f29acf8000p-5},
+{0x1.0732604ec956bp+0, -0x1.c63d19e9c0000p-6},
+{0x1.051980117f9b0p+0, -0x1.432ab6a388000p-6},
+{0x1.03091aa6810f1p+0, -0x1.8244357f50000p-7},
+{0x1.01010152cf066p+0, -0x1.0080a711c0000p-8},
+{0x1.fc07ef6b6e30bp-1, 0x1.fe03018e80000p-8},
+{0x1.f4465aa1024afp-1, 0x1.7b91986450000p-6},
+{0x1.ecc07a8fd3f5ep-1, 0x1.39e88608c8000p-5},
+{0x1.e573ad856b537p-1, 0x1.b42dc6e624000p-5},
+{0x1.de5d6dc7b8057p-1, 0x1.165372ec20000p-4},
+{0x1.d77b6498bddf7p-1, 0x1.51b07a0170000p-4},
+{0x1.d0cb580315c0fp-1, 0x1.8c3465c7ea000p-4},
+{0x1.ca4b30d1cf449p-1, 0x1.c5e544a290000p-4},
+{0x1.c3f8ef4810d8ep-1, 0x1.fec91aa0a6000p-4},
+{0x1.bdd2b8b311f44p-1, 0x1.1b72acdc5c000p-3},
+{0x1.b7d6c2eeac054p-1, 0x1.371fc65a98000p-3},
+{0x1.b20363474c8f5p-1, 0x1.526e61c1aa000p-3},
+{0x1.ac570165eeab1p-1, 0x1.6d60ffc240000p-3},
+{0x1.a6d019f331df4p-1, 0x1.87fa08a013000p-3},
+{0x1.a16d3ebc9e3c3p-1, 0x1.a23bc630c3000p-3},
+{0x1.9c2d14567ef45p-1, 0x1.bc286a3512000p-3},
+{0x1.970e4efae9169p-1, 0x1.d5c2195697000p-3},
+{0x1.920fb3bd0b802p-1, 0x1.ef0ae132d3000p-3},
+{0x1.8d3018b58699ap-1, 0x1.040259974e000p-2},
+{0x1.886e5ff170ee6p-1, 0x1.1058bd40e2000p-2},
+{0x1.83c977ad35d27p-1, 0x1.1c898c1137800p-2},
+{0x1.7f405ed16c520p-1, 0x1.2895a3e65b000p-2},
+{0x1.7ad220d0335c4p-1, 0x1.347dd8f6bd000p-2},
+{0x1.767dce53474fdp-1, 0x1.4043083cb3800p-2},
+#elif N == 128
{0x1.734f0c3e0de9fp+0, -0x1.7cc7f79e69000p-2},
{0x1.713786a2ce91fp+0, -0x1.76feec20d0000p-2},
{0x1.6f26008fab5a0p+0, -0x1.713e31351e000p-2},
@@ -212,7 +322,72 @@ that logc + poly(z/c - 1) has small error, however near x == 1 when
},
#ifndef __FP_FAST_FMA
.tab2 = {
-# if N == 128
+# if N == 64
+{0x1.61ffff94c4fecp-1, -0x1.9fe4fc998f325p-56},
+{0x1.66000020377ddp-1, 0x1.e804c7a9519f2p-55},
+{0x1.6a00004c41678p-1, 0x1.902c675d9ecfep-55},
+{0x1.6dffff7384f87p-1, -0x1.2fd6b95e55043p-56},
+{0x1.720000b37216ep-1, 0x1.802bc8d437043p-55},
+{0x1.75ffffbeb3c9dp-1, 0x1.6047ad0a0d4e4p-57},
+{0x1.7a0000628daep-1, -0x1.e00434b49313dp-56},
+{0x1.7dffffd7abd1ap-1, -0x1.6015f8a083576p-56},
+{0x1.81ffffdf40c54p-1, 0x1.7f54bf76a42c9p-57},
+{0x1.860000f334e11p-1, 0x1.60054cb5344d7p-56},
+{0x1.8a0001238aca7p-1, 0x1.c03c9bd132f55p-57},
+{0x1.8dffffb81d212p-1, -0x1.001e519f2764fp-55},
+{0x1.92000086adc7cp-1, 0x1.1fe40f88f49c6p-55},
+{0x1.960000135d8eap-1, -0x1.f832268dc3095p-55},
+{0x1.99ffff9435acp-1, 0x1.7031d8b835edcp-56},
+{0x1.9e00003478565p-1, -0x1.0030b221ce3eep-58},
+{0x1.a20000b592948p-1, 0x1.8fd2f1dbd4639p-55},
+{0x1.a600000ad0bcfp-1, 0x1.901d6a974e6bep-55},
+{0x1.a9ffff55953a5p-1, 0x1.a07556192db98p-57},
+{0x1.adffff29ce03dp-1, -0x1.fff0717ec71c2p-56},
+{0x1.b1ffff34f3ac8p-1, 0x1.8005573de89d1p-57},
+{0x1.b60000894c55bp-1, -0x1.ff2fb51b044c7p-57},
+{0x1.b9fffef45ec7dp-1, -0x1.9ff7c4e8730fp-56},
+{0x1.be0000cda7b2ap-1, 0x1.57d058dbf3c1dp-55},
+{0x1.c1ffff2c57917p-1, 0x1.7e66d7e48dbc9p-58},
+{0x1.c60000ea5b82ap-1, -0x1.47f5e132ed4bep-55},
+{0x1.ca0001121ae98p-1, -0x1.40958c8d5e00ap-58},
+{0x1.ce0000f9241cbp-1, -0x1.7da063caa81c8p-59},
+{0x1.d1fffe8be95a4p-1, -0x1.82e3a411afcd9p-59},
+{0x1.d5ffff035932bp-1, -0x1.00f901b3fe87dp-58},
+{0x1.d9fffe8b54ba7p-1, 0x1.ffef55d6e3a4p-55},
+{0x1.de0000ad95d19p-1, 0x1.5feb2efd4c7c7p-55},
+{0x1.e1fffe925ce47p-1, 0x1.c8085484eaf08p-55},
+{0x1.e5fffe3ddf853p-1, -0x1.fd5ed02c5cadp-60},
+{0x1.e9fffed0a0e5fp-1, -0x1.a80aaef411586p-55},
+{0x1.ee00008f82eep-1, -0x1.b000aeaf97276p-55},
+{0x1.f20000a22d2f4p-1, -0x1.8f8906e13eba3p-56},
+{0x1.f5fffee35b57dp-1, 0x1.1fdd33b2d3714p-57},
+{0x1.fa00014eec3a6p-1, -0x1.3ee0b7a18c1a5p-58},
+{0x1.fdffff5daa89fp-1, -0x1.c1e24c8e3b503p-58},
+{0x1.0200005b93349p+0, -0x1.50197fe6bedcap-54},
+{0x1.05ffff9d597acp+0, 0x1.20160d062d0dcp-55},
+{0x1.0a00005687a63p+0, -0x1.27f3f9307696ep-54},
+{0x1.0dffff779164ep+0, 0x1.b7eb40bb9c4f4p-54},
+{0x1.12000044a0aa8p+0, 0x1.efbc914d512c4p-55},
+{0x1.16000069685bcp+0, -0x1.c0bea3eb2d82cp-57},
+{0x1.1a000093f0d78p+0, 0x1.1fecbf1e8c52p-54},
+{0x1.1dffffb2b1457p+0, -0x1.3fc91365637d6p-55},
+{0x1.2200008824a1p+0, -0x1.dff7e9feb578ap-54},
+{0x1.25ffffeef953p+0, -0x1.b00a61ec912f7p-55},
+{0x1.2a0000a1e7783p+0, 0x1.60048318b0483p-56},
+{0x1.2e0000853d4c7p+0, -0x1.77fbedf2c8cf3p-54},
+{0x1.320000324c55bp+0, 0x1.f81983997354fp-54},
+{0x1.360000594f796p+0, -0x1.cfe4beff900a9p-54},
+{0x1.3a0000a4c1c0fp+0, 0x1.07dbb2e268d0ep-54},
+{0x1.3e0000751c61bp+0, 0x1.80583ed1c566ep-56},
+{0x1.42000069e8a9fp+0, 0x1.f01f1edf82045p-54},
+{0x1.460000b5a1e34p+0, -0x1.dfdf0cf45c14ap-55},
+{0x1.4a0000187e513p+0, 0x1.401306b83a98dp-55},
+{0x1.4dffff3ba420bp+0, 0x1.9fc6539a6454ep-56},
+{0x1.51fffffe391c9p+0, -0x1.601ef3353ac83p-54},
+{0x1.560000e342455p+0, 0x1.3fb7fac8ac151p-55},
+{0x1.59ffffc39676fp+0, 0x1.4fe7dd6659cc2p-55},
+{0x1.5dfffff10ef42p+0, -0x1.48154cb592bcbp-54},
+# elif N == 128
{0x1.61000014fb66bp-1, 0x1.e026c91425b3cp-56},
{0x1.63000034db495p-1, 0x1.dbfea48005d41p-55},
{0x1.650000d94d478p-1, 0x1.e7fa786d6a5b7p-55},
diff --git a/sysdeps/ieee754/dbl-64/math_config.h b/sysdeps/ieee754/dbl-64/math_config.h
index a74460b422..ea92cf313a 100644
--- a/sysdeps/ieee754/dbl-64/math_config.h
+++ b/sysdeps/ieee754/dbl-64/math_config.h
@@ -272,12 +272,11 @@ extern const struct log_data
double ln2lo;
double poly[LOG_POLY_ORDER - 1]; /* First coefficient is 1. */
double poly1[LOG_POLY1_ORDER - 1];
- /* See e_log_data.c for details. */
struct {double invc, logc;} tab[1 << LOG_TABLE_BITS];
#ifndef __FP_FAST_FMA
struct {double chi, clo;} tab2[1 << LOG_TABLE_BITS];
#endif
-} __log_data attribute_hidden;
+} __log_data __attribute__ ((__aligned__ (16))) attribute_hidden;
#define LOG2_TABLE_BITS 6
#define LOG2_POLY_ORDER 7
--
2.43.0
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