diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/compiler/glsl/builtin_functions.cpp | 18 |
1 files changed, 8 insertions, 10 deletions
diff --git a/src/compiler/glsl/builtin_functions.cpp b/src/compiler/glsl/builtin_functions.cpp index d77404ee77f..82e00a64ad9 100644 --- a/src/compiler/glsl/builtin_functions.cpp +++ b/src/compiler/glsl/builtin_functions.cpp @@ -5169,19 +5169,17 @@ builtin_builder::_tanh(const glsl_type *type) ir_variable *x = in_var(type, "x"); MAKE_SIG(type, v130, 1, x); - /* 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. + /* 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. */ ir_variable *t = body.make_temp(type, "tmp"); - body.emit(assign(t, min2(x, imm(10.0f)))); + body.emit(assign(t, min2(max2(x, imm(-10.0f)), imm(10.0f)))); - body.emit(ret(div(sub(exp(mul(t, imm(2.0f))), imm(1.0f)), - add(exp(mul(t, imm(2.0f))), imm(1.0f))))); + /* (e^x - e^(-x)) / (e^x + e^(-x)) */ + body.emit(ret(div(sub(exp(t), exp(neg(t))), + add(exp(t), exp(neg(t)))))); return sig; } |