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Length: 3072 (0xc00)
Types: Ada Source
Notes: 03_class, FILE, R1k_Segment, e3_tag, function Tanh, seg_0130e5, separate Generic_Elementary_Functions
└─⟦8527c1e9b⟧ Bits:30000544 8mm tape, Rational 1000, Arrival backup of disks in PAM's R1000
└─ ⟦cfc2e13cd⟧ »Space Info Vol 2«
└─⟦this⟧
separate (Generic_Elementary_Functions)
function Tanh (X : Float_Type) return Float_Type is
-- On input, X is a floating-point value in Float_Type;
-- On output, the value of tanh(X) (the hyperbolic tangent of X) is returned.
-- The definition of tanh(Y) is sinh(Y)/cosh(Y), which is also equivalent
-- to the following three formulas.
-- 1. ( exp(Y) - exp(-Y) ) / ( exp(Y) + exp(-Y) )
-- 2. ( 1 - ( 2 / ( exp(2*Y) + 1 ) ) )
-- 3. ( exp(2*Y) - 1 ) / ( exp(2*Y) + 1 ).
-- but computationally, some formulas are better on some ranges.
Z, Sign_Y : Common_Float;
Y, Abs_Y : Common_Float;
Log2 : constant Common_Float := 16#0.B17217F7D1CF79ABC9E3B39803F2F6AF40#;
Base_Digits : constant Common_Float :=
Common_Float (6 * Float_Type'Base'Digits);
Log2_Times_2 : constant Common_Float := (2.0 * Log2);
Cond : constant Common_Float := (Base_Digits * Log2);
begin
-- Filter out exceptional cases.
if (X = 0.0) then
return (X);
end if;
Y := Common_Float (X);
Abs_Y := abs (Y);
if (Y >= 0.0) then
Sign_Y := 1.0;
else
Sign_Y := -1.0;
end if;
if (Abs_Y <= (Log2_Times_2)) then
-- Formula 3 should be used in this situation to guarantee accuracy.
Z := Kf_Em1 (2.0 * Abs_Y);
Z := Sign_Y * (Z / (Z + 2.0));
return (Float_Type (Z));
elsif (Abs_Y > Cond) then
-- Formula 2 should be used in this situation to guarantee accuracy,
-- but observe that 2/(exp(2*Y) + 1) will be so small compared to 1
-- that it is negligible.
return (Float_Type (Sign_Y));
else
-- When ( Log2_Times_2 < Abs_Y <= Cond ), use formula 2 for best accuracy.
Z := Kf_Em1 (2.0 * Abs_Y);
Z := Sign_Y * (1.0 - 2.0 / (Z + 2.0));
return (Float_Type (Z));
end if;
end Tanh;
nblk1=2
nid=0
hdr6=4
[0x00] rec0=22 rec1=00 rec2=01 rec3=010
[0x01] rec0=2a rec1=00 rec2=02 rec3=000
tail 0x2170e746682b1523627e0 0x42a00066462061e03