https://github.com/wenju-he updated https://github.com/llvm/llvm-project/pull/179875
>From 85b513d282e3006973af015c0682cedc24ae1515 Mon Sep 17 00:00:00 2001 From: Wenju He <[email protected]> Date: Thu, 5 Feb 2026 07:31:07 +0100 Subject: [PATCH 1/3] [libclc] Fix exp and exp2 float implementation subnormal handling Float implementation fail OpenCL CTS on intel gpu: ERROR: exp: -8377325.500000 ulp error at -0x1.5d5ap+6 (0xc2aead00): *0x1.ff4fb8p-127 vs. 0x0p+0 ERROR: exp2: -8377259.000000 ulp error at -0x1.f802p+6 (0xc2fc0100): *0x1.ff4eacp-127 vs. 0x0p+0 Root cause: * `Scale by 2^p` doesn't work if p is smaller than -126 (subnormal range). * llim check flushes subnormal result to 0. Fix by splitting the exponent to preserves subnormal results and lowering llim to the smallest subnormal range. --- libclc/clc/lib/generic/math/clc_exp.inc | 13 +++++++++---- libclc/clc/lib/generic/math/clc_exp2.inc | 10 +++++++--- 2 files changed, 16 insertions(+), 7 deletions(-) diff --git a/libclc/clc/lib/generic/math/clc_exp.inc b/libclc/clc/lib/generic/math/clc_exp.inc index 5057bf8034e92..c6131c55690ae 100644 --- a/libclc/clc/lib/generic/math/clc_exp.inc +++ b/libclc/clc/lib/generic/math/clc_exp.inc @@ -37,16 +37,21 @@ _CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE __clc_exp(__CLC_GENTYPE x) { __CLC_GENTYPE y = 1.0f - (((-lo) - MATH_DIVIDE(t * v, 2.0f - v)) - hi); - // Scale by 2^p - __CLC_GENTYPE r = __CLC_AS_GENTYPE(__CLC_AS_INTN(y) + (p << 23)); + // Split the exponent to preserves subnormal results when p is very negative. + __CLC_INTN p1 = p / 2; + __CLC_INTN p2 = p - p1; + __CLC_GENTYPE s1 = __CLC_AS_GENTYPE((p1 + 127) << 23); + __CLC_GENTYPE s2 = __CLC_AS_GENTYPE((p2 + 127) << 23); + __CLC_GENTYPE r = y * s1 * s2; // ln(largest_normal) = 88.72283905206835305366 const __CLC_GENTYPE ulim = 0x1.62e430p+6f; - // ln(smallest_normal) = -87.33654475055310898657 - const __CLC_GENTYPE llim = -0x1.5d589ep+6f; + // ln(smallest_subnormal) + const __CLC_GENTYPE llim = -0x1.9d1da0p+6f; r = x < llim ? 0.0f : r; r = x < ulim ? r : __CLC_AS_GENTYPE((__CLC_UINTN)0x7f800000); + return __clc_isnan(x) ? x : r; } diff --git a/libclc/clc/lib/generic/math/clc_exp2.inc b/libclc/clc/lib/generic/math/clc_exp2.inc index 6da361a43ed4c..8526dcb81feda 100644 --- a/libclc/clc/lib/generic/math/clc_exp2.inc +++ b/libclc/clc/lib/generic/math/clc_exp2.inc @@ -36,11 +36,15 @@ _CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE __clc_exp2(__CLC_GENTYPE x) { __CLC_GENTYPE y = 1.0f - (((-lo) - MATH_DIVIDE(t * v, 2.0f - v)) - hi); - // Scale by 2^p - __CLC_GENTYPE r = __CLC_AS_FLOATN(__CLC_AS_INTN(y) + (p << 23)); + // Split the exponent to preserves subnormal results when p is very negative. + __CLC_INTN p1 = p / 2; + __CLC_INTN p2 = p - p1; + __CLC_GENTYPE s1 = __CLC_AS_GENTYPE((p1 + 127) << 23); + __CLC_GENTYPE s2 = __CLC_AS_GENTYPE((p2 + 127) << 23); + __CLC_GENTYPE r = y * s1 * s2; const __CLC_GENTYPE ulim = 128.0f; - const __CLC_GENTYPE llim = -126.0f; + const __CLC_GENTYPE llim = -149.0f; r = x < llim ? 0.0f : r; r = x < ulim ? r : __CLC_AS_FLOATN((__CLC_UINTN)0x7f800000); >From 61adcb24dfbee4822250da963948a67bdb03c770 Mon Sep 17 00:00:00 2001 From: Wenju He <[email protected]> Date: Thu, 5 Feb 2026 09:31:42 +0100 Subject: [PATCH 2/3] use right shift --- libclc/clc/lib/generic/math/clc_exp.inc | 2 +- libclc/clc/lib/generic/math/clc_exp2.inc | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/libclc/clc/lib/generic/math/clc_exp.inc b/libclc/clc/lib/generic/math/clc_exp.inc index c6131c55690ae..ef836ce35a7a3 100644 --- a/libclc/clc/lib/generic/math/clc_exp.inc +++ b/libclc/clc/lib/generic/math/clc_exp.inc @@ -38,7 +38,7 @@ _CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE __clc_exp(__CLC_GENTYPE x) { __CLC_GENTYPE y = 1.0f - (((-lo) - MATH_DIVIDE(t * v, 2.0f - v)) - hi); // Split the exponent to preserves subnormal results when p is very negative. - __CLC_INTN p1 = p / 2; + __CLC_INTN p1 = p >> 1; __CLC_INTN p2 = p - p1; __CLC_GENTYPE s1 = __CLC_AS_GENTYPE((p1 + 127) << 23); __CLC_GENTYPE s2 = __CLC_AS_GENTYPE((p2 + 127) << 23); diff --git a/libclc/clc/lib/generic/math/clc_exp2.inc b/libclc/clc/lib/generic/math/clc_exp2.inc index 8526dcb81feda..6520c69e94601 100644 --- a/libclc/clc/lib/generic/math/clc_exp2.inc +++ b/libclc/clc/lib/generic/math/clc_exp2.inc @@ -37,7 +37,7 @@ _CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE __clc_exp2(__CLC_GENTYPE x) { __CLC_GENTYPE y = 1.0f - (((-lo) - MATH_DIVIDE(t * v, 2.0f - v)) - hi); // Split the exponent to preserves subnormal results when p is very negative. - __CLC_INTN p1 = p / 2; + __CLC_INTN p1 = p >> 1; __CLC_INTN p2 = p - p1; __CLC_GENTYPE s1 = __CLC_AS_GENTYPE((p1 + 127) << 23); __CLC_GENTYPE s2 = __CLC_AS_GENTYPE((p2 + 127) << 23); >From 4298d516f5b0d334953baa27603231b677695e82 Mon Sep 17 00:00:00 2001 From: Wenju He <[email protected]> Date: Fri, 6 Feb 2026 07:09:15 +0100 Subject: [PATCH 3/3] add back original comment --- libclc/clc/lib/generic/math/clc_exp.inc | 1 + libclc/clc/lib/generic/math/clc_exp2.inc | 1 + 2 files changed, 2 insertions(+) diff --git a/libclc/clc/lib/generic/math/clc_exp.inc b/libclc/clc/lib/generic/math/clc_exp.inc index ef836ce35a7a3..786b4a4f5cd52 100644 --- a/libclc/clc/lib/generic/math/clc_exp.inc +++ b/libclc/clc/lib/generic/math/clc_exp.inc @@ -37,6 +37,7 @@ _CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE __clc_exp(__CLC_GENTYPE x) { __CLC_GENTYPE y = 1.0f - (((-lo) - MATH_DIVIDE(t * v, 2.0f - v)) - hi); + // Scale by 2^p // Split the exponent to preserves subnormal results when p is very negative. __CLC_INTN p1 = p >> 1; __CLC_INTN p2 = p - p1; diff --git a/libclc/clc/lib/generic/math/clc_exp2.inc b/libclc/clc/lib/generic/math/clc_exp2.inc index 6520c69e94601..ac5a86f87d754 100644 --- a/libclc/clc/lib/generic/math/clc_exp2.inc +++ b/libclc/clc/lib/generic/math/clc_exp2.inc @@ -36,6 +36,7 @@ _CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE __clc_exp2(__CLC_GENTYPE x) { __CLC_GENTYPE y = 1.0f - (((-lo) - MATH_DIVIDE(t * v, 2.0f - v)) - hi); + // Scale by 2^p // Split the exponent to preserves subnormal results when p is very negative. __CLC_INTN p1 = p >> 1; __CLC_INTN p2 = p - p1; _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
