1 /* $NetBSD: ldexp.S,v 1.9 2009/12/14 01:07:42 matt Exp $ */
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37 #if defined(LIBC_SCCS) && !defined(lint)
39 RCSID("from: @(#)ldexp.s 8.1 (Berkeley) 6/4/93")
41 RCSID("$NetBSD: ldexp.S,v 1.9 2009/12/14 01:07:42 matt Exp $")
43 #endif /* LIBC_SCCS and not lint */
45 #define DEXP_INF 0x7ff
46 #define DEXP_BIAS 1023
47 #define DEXP_MIN -1022
50 #define DIMPL_ONE 0x00100000
51 #define DLEAD_ZEROS 31 - 20
53 #define GUARDBIT 0x80000000
54 #define DSIGNAL_NAN 0x00040000
55 #define DQUIET_NAN0 0x0007ffff
56 #define DQUIET_NAN1 0xffffffff
62 * Return x * (2**N), for integer values N.
65 mfc1 v1, $f13 # get MSW of x
66 mfc1 t3, $f12 # get LSW of x
67 sll t1, v1, 1 # get x exponent
69 beq t1, DEXP_INF, 9f # is it a NAN or infinity?
70 beq t1, zero, 1f # zero or denormalized number?
71 addu t1, t1, a2 # scale exponent
72 sll v0, a2, 20 # position N for addition
73 bge t1, DEXP_INF, 8f # overflow?
74 addu v0, v0, v1 # multiply by (2**N)
75 ble t1, zero, 4f # underflow?
76 mtc1 v0, $f1 # save MSW of result
77 mtc1 t3, $f0 # save LSW of result
80 sll t2, v1, 32 - 20 # get x fraction
82 srl t0, v1, 31 # get x sign
84 beq t3, zero, 9f # result is zero
87 * Find out how many leading zero bits are in t2,t3 and put in t9.
119 * Now shift t2,t3 the correct number of bits.
122 subu t9, t9, DLEAD_ZEROS # dont count normal leading zeros
123 li t1, DEXP_MIN + DEXP_BIAS
124 subu t1, t1, t9 # adjust exponent
125 addu t1, t1, a2 # scale exponent
128 subu t9, t9, v0 # shift fraction left >= 32 bits
133 subu v0, v0, t9 # shift fraction left < 32 bits
139 bge t1, DEXP_INF, 8f # overflow?
140 ble t1, zero, 4f # underflow?
141 sll t2, t2, 32 - 20 # clear implied one bit
144 sll t1, t1, 31 - 11 # reposition exponent
145 sll t0, t0, 31 # reposition sign
146 or t0, t0, t1 # put result back together
148 mtc1 t0, $f1 # save MSW of result
149 mtc1 t3, $f0 # save LSW of result
153 ble t1, -52, 7f # is result too small for denorm?
154 sll t2, v1, 31 - 20 # clear exponent, extract fraction
155 or t2, t2, v0 # set implied one bit
156 blt t1, -30, 2f # will all bits in t3 be shifted out?
157 srl t2, t2, 31 - 20 # shift fraction back to normal position
159 sll ta0, t2, t1 # shift right t2,t3 based on exponent
160 srl t8, t3, t1 # save bits shifted out
165 bge t8, zero, 1f # does result need to be rounded?
166 addu t3, t3, 1 # round result
170 bne t8, zero, 1f # round result to nearest
173 mtc1 t3, $f0 # save denormalized result (LSW)
174 mtc1 t2, $f1 # save denormalized result (MSW)
175 bge v1, zero, 1f # should result be negative?
176 neg.d $f0, $f0 # negate result
180 mtc1 zero, $f1 # exponent and upper fraction
181 addu t1, t1, 20 # compute amount to shift right by
182 sll t8, t2, t1 # save bits shifted out
185 bge t8, zero, 1f # does result need to be rounded?
186 addu t3, t3, 1 # round result
189 mtc1 ta0, $f1 # exponent and upper fraction
190 bne t8, zero, 1f # round result to nearest
194 bge v1, zero, 1f # is result negative?
195 neg.d $f0, $f0 # negate result
199 mtc1 zero, $f0 # result is zero
201 beq t0, zero, 1f # is result positive?
202 neg.d $f0, $f0 # negate result
206 li t1, 0x7ff00000 # result is infinity (MSW)
208 mtc1 zero, $f0 # result is infinity (LSW)
209 bge v1, zero, 1f # should result be negative infinity?
210 neg.d $f0, $f0 # result is negative infinity
212 add.d $f0, $f0 # cause overflow faults if enabled
215 mov.d $f0, $f12 # yes, result is just x