diff options
Diffstat (limited to 'src/compiler/glsl')
| -rw-r--r-- | src/compiler/glsl/builtin_functions.cpp | 18 |
1 files changed, 10 insertions, 8 deletions
diff --git a/src/compiler/glsl/builtin_functions.cpp b/src/compiler/glsl/builtin_functions.cpp index 3dead1af00f..17f03a3fa27 100644 --- a/src/compiler/glsl/builtin_functions.cpp +++ b/src/compiler/glsl/builtin_functions.cpp @@ -3563,17 +3563,19 @@ builtin_builder::_tanh(const glsl_type *type) ir_variable *x = in_var(type, "x"); MAKE_SIG(type, v130, 1, x); - /* Clamp x to [-10, +10] to avoid precision problems. - * When x > 10, e^(-x) is so small relative to e^x that it gets flushed to - * zero in the computation e^x + e^(-x). The same happens in the other - * direction when x < -10. + /* tanh(x) := (0.5 * (e^x - e^(-x))) / (0.5 * (e^x + e^(-x))) + * + * With a little algebra this reduces to (e^2x - 1) / (e^2x + 1) + * + * Clamp x to (-inf, +10] to avoid precision problems. When x > 10, e^2x + * is so much larger than 1.0 that 1.0 gets flushed to zero in the + * computation e^2x +/- 1 so it can be ignored. */ ir_variable *t = body.make_temp(type, "tmp"); - body.emit(assign(t, min2(max2(x, imm(-10.0f)), imm(10.0f)))); + body.emit(assign(t, min2(x, imm(10.0f)))); - /* (e^x - e^(-x)) / (e^x + e^(-x)) */ - body.emit(ret(div(sub(exp(t), exp(neg(t))), - add(exp(t), exp(neg(t)))))); + body.emit(ret(div(sub(exp(mul(t, imm(2.0f))), imm(1.0f)), + add(exp(mul(t, imm(2.0f))), imm(1.0f))))); return sig; } |