1 /* $NetBSD: ldexp.S,v 1.8 2003/08/07 16:42:15 agc Exp $ */
4 * Copyright (c) 1991, 1993
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35 #include <machine/asm.h>
36 __FBSDID("$FreeBSD$");
38 #if defined(LIBC_SCCS) && !defined(lint)
39 ASMSTR("from: @(#)ldexp.s 8.1 (Berkeley) 6/4/93")
40 ASMSTR("$NetBSD: ldexp.S,v 1.8 2003/08/07 16:42:15 agc Exp $")
41 #endif /* LIBC_SCCS and not lint */
47 #define DEXP_INF 0x7ff
48 #define DEXP_BIAS 1023
49 #define DEXP_MIN -1022
52 #define DIMPL_ONE 0x00100000
53 #define DLEAD_ZEROS 31 - 20
55 #define GUARDBIT 0x80000000
56 #define DSIGNAL_NAN 0x00040000
57 #define DQUIET_NAN0 0x0007ffff
58 #define DQUIET_NAN1 0xffffffff
64 * Return x * (2**N), for integer values N.
67 mfc1 v1, $f13 # get MSW of x
68 mfc1 t3, $f12 # get LSW of x
69 sll t1, v1, 1 # get x exponent
71 beq t1, DEXP_INF, 9f # is it a NAN or infinity?
72 beq t1, zero, 1f # zero or denormalized number?
73 addu t1, t1, a2 # scale exponent
74 sll v0, a2, 20 # position N for addition
75 bge t1, DEXP_INF, 8f # overflow?
76 addu v0, v0, v1 # multiply by (2**N)
77 ble t1, zero, 4f # underflow?
78 mtc1 v0, $f1 # save MSW of result
79 mtc1 t3, $f0 # save LSW of result
82 sll t2, v1, 32 - 20 # get x fraction
84 srl t0, v1, 31 # get x sign
86 beq t3, zero, 9f # result is zero
89 * Find out how many leading zero bits are in t2,t3 and put in t9.
121 * Now shift t2,t3 the correct number of bits.
124 subu t9, t9, DLEAD_ZEROS # dont count normal leading zeros
125 li t1, DEXP_MIN + DEXP_BIAS
126 subu t1, t1, t9 # adjust exponent
127 addu t1, t1, a2 # scale exponent
130 subu t9, t9, v0 # shift fraction left >= 32 bits
135 subu v0, v0, t9 # shift fraction left < 32 bits
141 bge t1, DEXP_INF, 8f # overflow?
142 ble t1, zero, 4f # underflow?
143 sll t2, t2, 32 - 20 # clear implied one bit
146 sll t1, t1, 31 - 11 # reposition exponent
147 sll t0, t0, 31 # reposition sign
148 or t0, t0, t1 # put result back together
150 mtc1 t0, $f1 # save MSW of result
151 mtc1 t3, $f0 # save LSW of result
155 ble t1, -52, 7f # is result too small for denorm?
156 sll t2, v1, 31 - 20 # clear exponent, extract fraction
157 or t2, t2, v0 # set implied one bit
158 blt t1, -30, 2f # will all bits in t3 be shifted out?
159 srl t2, t2, 31 - 20 # shift fraction back to normal position
161 sll ta0, t2, t1 # shift right t2,t3 based on exponent
162 srl t8, t3, t1 # save bits shifted out
167 bge t8, zero, 1f # does result need to be rounded?
168 addu t3, t3, 1 # round result
172 bne t8, zero, 1f # round result to nearest
175 mtc1 t3, $f0 # save denormalized result (LSW)
176 mtc1 t2, $f1 # save denormalized result (MSW)
177 bge v1, zero, 1f # should result be negative?
178 neg.d $f0, $f0 # negate result
182 mtc1 zero, $f1 # exponent and upper fraction
183 addu t1, t1, 20 # compute amount to shift right by
184 sll t8, t2, t1 # save bits shifted out
187 bge t8, zero, 1f # does result need to be rounded?
188 addu t3, t3, 1 # round result
191 mtc1 ta0, $f1 # exponent and upper fraction
192 bne t8, zero, 1f # round result to nearest
196 bge v1, zero, 1f # is result negative?
197 neg.d $f0, $f0 # negate result
201 mtc1 zero, $f0 # result is zero
203 beq t0, zero, 1f # is result positive?
204 neg.d $f0, $f0 # negate result
208 li t1, 0x7ff00000 # result is infinity (MSW)
210 mtc1 zero, $f0 # result is infinity (LSW)
211 bge v1, zero, 1f # should result be negative infinity?
212 neg.d $f0, $f0 # result is negative infinity
214 add.d $f0, $f0 # cause overflow faults if enabled
217 mov.d $f0, $f12 # yes, result is just x