arch/m68k/fpsp040/stanh.S

Source file repositories/reference/linux-study-clean/arch/m68k/fpsp040/stanh.S

File Facts

System
Linux kernel
Corpus path
arch/m68k/fpsp040/stanh.S
Extension
.S
Size
4074 bytes
Lines
185
Domain
Architecture Layer
Bucket
arch/m68k
Inferred role
Architecture Layer: arch/m68k
Status
atlas-only

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

|
|	stanh.sa 3.1 12/10/90
|
|	The entry point sTanh computes the hyperbolic tangent of
|	an input argument; sTanhd does the same except for denormalized
|	input.
|
|	Input: Double-extended number X in location pointed to
|		by address register a0.
|
|	Output: The value tanh(X) returned in floating-point register Fp0.
|
|	Accuracy and Monotonicity: The returned result is within 3 ulps in
|		64 significant bit, i.e. within 0.5001 ulp to 53 bits if the
|		result is subsequently rounded to double precision. The
|		result is provably monotonic in double precision.
|
|	Speed: The program stanh takes approximately 270 cycles.
|
|	Algorithm:
|
|	TANH
|	1. If |X| >= (5/2) log2 or |X| <= 2**(-40), go to 3.
|
|	2. (2**(-40) < |X| < (5/2) log2) Calculate tanh(X) by
|		sgn := sign(X), y := 2|X|, z := expm1(Y), and
|		tanh(X) = sgn*( z/(2+z) ).
|		Exit.
|
|	3. (|X| <= 2**(-40) or |X| >= (5/2) log2). If |X| < 1,
|		go to 7.
|
|	4. (|X| >= (5/2) log2) If |X| >= 50 log2, go to 6.
|
|	5. ((5/2) log2 <= |X| < 50 log2) Calculate tanh(X) by
|		sgn := sign(X), y := 2|X|, z := exp(Y),
|		tanh(X) = sgn - [ sgn*2/(1+z) ].
|		Exit.
|
|	6. (|X| >= 50 log2) Tanh(X) = +-1 (round to nearest). Thus, we
|		calculate Tanh(X) by
|		sgn := sign(X), Tiny := 2**(-126),
|		tanh(X) := sgn - sgn*Tiny.
|		Exit.
|
|	7. (|X| < 2**(-40)). Tanh(X) = X.	Exit.
|

|		Copyright (C) Motorola, Inc. 1990
|			All Rights Reserved
|
|       For details on the license for this file, please see the
|       file, README, in this same directory.

|STANH	idnt	2,1 | Motorola 040 Floating Point Software Package

	|section	8

#include "fpsp.h"

	.set	X,FP_SCR5
	.set	XDCARE,X+2
	.set	XFRAC,X+4

	.set	SGN,L_SCR3

	.set	V,FP_SCR6

BOUNDS1:	.long 0x3FD78000,0x3FFFDDCE | ... 2^(-40), (5/2)LOG2

Annotation

Implementation Notes