1 /* ix87 specific implementation of exp(x)-1.
2 Copyright (C) 1996-2024 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
19 /* Using: e^x - 1 = 2^(x * log2(e)) - 1 */
22 #include <machine/asm.h>
23 #include <i386-math-asm.h>
24 #include <libm-alias-double.h>
31 ASM_SIZE_DIRECTIVE(minus1)
34 ASM_SIZE_DIRECTIVE(one)
36 l2e: .quad 0xb8aa3b295c17f0bc /* 1.442695040888963407359924681002 */
38 ASM_SIZE_DIRECTIVE(l2e)
43 #define MO(op) op##@GOTOFF(%edx)
50 movzwl 4+6(%esp), %eax
51 xorb $0x80, %ah // invert sign bit (now 1 is "positive")
52 cmpl $0xc086, %eax // is num >= 704?
53 jae HIDDEN_JUMPTARGET (__exp)
56 fxam // Is NaN, +-Inf or +-0?
58 cmpl $0xc043, %eax // is num <= -38.0?
63 // Below -38.0 (may be -NaN or -Inf).
69 je 5f // If -NaN, jump.
70 jmp 2f // -large, possibly -Inf.
72 4: // In range -38.0 to 704.0 (may be +-0 but not NaN or +-Inf).
75 je 3f // If +-0, jump.
80 5: fldt MO(l2e) // log2(e) : x
82 fld %st // log2(e)*x : log2(e)*x
83 // Set round-to-nearest temporarily.
85 cfi_adjust_cfa_offset (8)
91 frndint // int(log2(e)*x) : log2(e)*x
94 cfi_adjust_cfa_offset (-8)
95 fsubr %st, %st(1) // int(log2(e)*x) : fract(log2(e)*x)
96 fxch // fract(log2(e)*x) : int(log2(e)*x)
97 f2xm1 // 2^fract(log2(e)*x)-1 : int(log2(e)*x)
98 fscale // 2^(log2(e)*x)-2^int(log2(e)*x) : int(log2(e)*x)
99 fxch // int(log2(e)*x) : 2^(log2(e)*x)-2^int(log2(e)*x)
100 fldl MO(one) // 1 : int(log2(e)*x) : 2^(log2(e)*x)-2^int(log2(e)*x)
101 fscale // 2^int(log2(e)*x) : int(log2(e)*x) : 2^(log2(e)*x)-2^int(log2(e)*x)
102 fsubrl MO(one) // 1-2^int(log2(e)*x) : int(log2(e)*x) : 2^(log2(e)*x)-2^int(log2(e)*x)
103 fstp %st(1) // 1-2^int(log2(e)*x) : 2^(log2(e)*x)-2^int(log2(e)*x)
104 fsubrp %st, %st(1) // 2^(log2(e)*x)
105 DBL_CHECK_FORCE_UFLOW
109 fldl MO(minus1) // Set result to -1.0.
112 libm_alias_double (__expm1, expm1)