https://github.com/rjodinchr updated
https://github.com/llvm/llvm-project/pull/132390
>From 95eeda421b4cdc468f828d36146d609e80d195d9 Mon Sep 17 00:00:00 2001
From: Romaric Jodin <rjo...@google.com>
Date: Fri, 21 Mar 2025 13:51:41 +0100
Subject: [PATCH 1/2] libclc: erfc: fix fp32 implementation
On some implementation, the current implementation lead to slight
accuracy issues.
While the maths behing this implementation is correct, it does not
take into account the accumulation of errors coming from other
operators that do not provide correct rounding (like the exp
function).
To avoid it, compute staticaly exp(-0.5625).
Fix #124939
---
libclc/generic/lib/math/erf.cl | 11 ++++++-----
libclc/generic/lib/math/erfc.cl | 11 ++++++-----
2 files changed, 12 insertions(+), 10 deletions(-)
diff --git a/libclc/generic/lib/math/erf.cl b/libclc/generic/lib/math/erf.cl
index 8349f306a63f7..79fdecdc866fd 100644
--- a/libclc/generic/lib/math/erf.cl
+++ b/libclc/generic/lib/math/erf.cl
@@ -23,7 +23,7 @@
#define erx 8.4506291151e-01f /* 0x3f58560b */
-// Coefficients for approximation to erf on [00.84375]
+// Coefficients for approximation to erf on [0, 0.84375]
#define efx 1.2837916613e-01f /* 0x3e0375d4 */
#define efx8 1.0270333290e+00f /* 0x3f8375d4 */
@@ -39,7 +39,7 @@
#define qq4 1.3249473704e-04f /* 0x390aee49 */
#define qq5 -3.9602282413e-06f /* 0xb684e21a */
-// Coefficients for approximation to erf in [0.843751.25]
+// Coefficients for approximation to erf in [0.84375, 1.25]
#define pa0 -2.3621185683e-03f /* 0xbb1acdc6 */
#define pa1 4.1485610604e-01f /* 0x3ed46805 */
@@ -55,7 +55,7 @@
#define qa5 1.3637083583e-02f /* 0x3c5f6e13 */
#define qa6 1.1984500103e-02f /* 0x3c445aa3 */
-// Coefficients for approximation to erfc in [1.251/0.35]
+// Coefficients for approximation to erfc in [1.25, 1/0.35]
#define ra0 -9.8649440333e-03f /* 0xbc21a093 */
#define ra1 -6.9385856390e-01f /* 0xbf31a0b7 */
@@ -74,7 +74,7 @@
#define sa7 6.5702495575e+00f /* 0x40d23f7c */
#define sa8 -6.0424413532e-02f /* 0xbd777f97 */
-// Coefficients for approximation to erfc in [1/.3528]
+// Coefficients for approximation to erfc in [1/0.35, 28]
#define rb0 -9.8649431020e-03f /* 0xbc21a092 */
#define rb1 -7.9928326607e-01f /* 0xbf4c9dd4 */
@@ -130,7 +130,8 @@ _CLC_OVERLOAD _CLC_DEF float erf(float x) {
// |x| < 6
float z = as_float(ix & 0xfffff000);
- float r = exp(mad(-z, z, -0.5625f)) * exp(mad(z-absx, z+absx, q));
+ float r = exp(-z * z) * exp(mad(z - absx, z + absx, q));
+ r *= 0x1.23ba94p-1; // exp(-0.5625)
r = 1.0f - MATH_DIVIDE(r, absx);
ret = absx < 6.0f ? r : ret;
diff --git a/libclc/generic/lib/math/erfc.cl b/libclc/generic/lib/math/erfc.cl
index 01526d7ae1eb5..05492972ed434 100644
--- a/libclc/generic/lib/math/erfc.cl
+++ b/libclc/generic/lib/math/erfc.cl
@@ -23,7 +23,7 @@
#define erx_f 8.4506291151e-01f /* 0x3f58560b */
-// Coefficients for approximation to erf on [00.84375]
+// Coefficients for approximation to erf on [0, 0.84375]
#define efx 1.2837916613e-01f /* 0x3e0375d4 */
#define efx8 1.0270333290e+00f /* 0x3f8375d4 */
@@ -39,7 +39,7 @@
#define qq4 1.3249473704e-04f /* 0x390aee49 */
#define qq5 -3.9602282413e-06f /* 0xb684e21a */
-// Coefficients for approximation to erf in [0.843751.25]
+// Coefficients for approximation to erf in [0.84375, 1.25]
#define pa0 -2.3621185683e-03f /* 0xbb1acdc6 */
#define pa1 4.1485610604e-01f /* 0x3ed46805 */
@@ -55,7 +55,7 @@
#define qa5 1.3637083583e-02f /* 0x3c5f6e13 */
#define qa6 1.1984500103e-02f /* 0x3c445aa3 */
-// Coefficients for approximation to erfc in [1.251/0.35]
+// Coefficients for approximation to erfc in [1.25, 1/0.35]
#define ra0 -9.8649440333e-03f /* 0xbc21a093 */
#define ra1 -6.9385856390e-01f /* 0xbf31a0b7 */
@@ -74,7 +74,7 @@
#define sa7 6.5702495575e+00f /* 0x40d23f7c */
#define sa8 -6.0424413532e-02f /* 0xbd777f97 */
-// Coefficients for approximation to erfc in [1/.3528]
+// Coefficients for approximation to erfc in [1/0.35, 28]
#define rb0 -9.8649431020e-03f /* 0xbc21a092 */
#define rb1 -7.9928326607e-01f /* 0xbf4c9dd4 */
@@ -131,7 +131,8 @@ _CLC_OVERLOAD _CLC_DEF float erfc(float x) {
float ret = 0.0f;
float z = as_float(ix & 0xfffff000);
- float r = exp(mad(-z, z, -0.5625f)) * exp(mad(z - absx, z + absx, q));
+ float r = exp(-z * z) * exp(mad(z - absx, z + absx, q));
+ r *= 0x1.23ba94p-1; // exp(-0.5625)
r = MATH_DIVIDE(r, absx);
t = 2.0f - r;
r = x < 0.0f ? t : r;
>From 7a1304bb1fef5175a4c27e83872d68ac9cb0b606 Mon Sep 17 00:00:00 2001
From: Romaric Jodin <rjo...@chromium.org>
Date: Mon, 24 Mar 2025 16:00:22 +0100
Subject: [PATCH 2/2] Update libclc/generic/lib/math/erfc.cl
Co-authored-by: Fraser Cormack <frasercr...@gmail.com>
---
libclc/generic/lib/math/erfc.cl | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libclc/generic/lib/math/erfc.cl b/libclc/generic/lib/math/erfc.cl
index 05492972ed434..4818de64536fb 100644
--- a/libclc/generic/lib/math/erfc.cl
+++ b/libclc/generic/lib/math/erfc.cl
@@ -132,7 +132,7 @@ _CLC_OVERLOAD _CLC_DEF float erfc(float x) {
float z = as_float(ix & 0xfffff000);
float r = exp(-z * z) * exp(mad(z - absx, z + absx, q));
- r *= 0x1.23ba94p-1; // exp(-0.5625)
+ r *= 0x1.23ba94p-1f; // exp(-0.5625)
r = MATH_DIVIDE(r, absx);
t = 2.0f - r;
r = x < 0.0f ? t : r;
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
