1// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
2// See https://llvm.org/LICENSE.txt for license information.
3// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
4
5#include "../assembly.h"
6
7// float __floatundisf(du_int a);
8
9// Note that there is a hardware instruction, fildll, that does most of what
10// this function needs to do. However, because of our ia32 ABI, it will take
11// a write-small read-large stall, so the software implementation here is
12// actually several cycles faster.
13
14// This is a branch-free implementation. A branchy implementation might be
15// faster for the common case if you know something a priori about the input
16// distribution.
17
18/* branch-free x87 implementation - one cycle slower than without x87.
19
20#ifdef __i386__
21
22CONST_SECTION
23.balign 3
24
25 .quad 0x43f0000000000000
26twop64: .quad 0x0000000000000000
27
28#define TWOp64 twop64-0b(%ecx,%eax,8)
29
30.text
31.balign 4
32DEFINE_COMPILERRT_FUNCTION(__floatundisf)
33 movl 8(%esp), %eax
34 movd 8(%esp), %xmm1
35 movd 4(%esp), %xmm0
36 punpckldq %xmm1, %xmm0
37 calll 0f
380: popl %ecx
39 sarl $31, %eax
40 movq %xmm0, 4(%esp)
41 fildll 4(%esp)
42 faddl TWOp64
43 fstps 4(%esp)
44 flds 4(%esp)
45 ret
46END_COMPILERRT_FUNCTION(__floatundisf)
47
48#endif // __i386__
49
50*/
51
52// branch-free, x87-free implementation - faster at the expense of code size
53
54#ifdef __i386__
55
56CONST_SECTION
57
58 .balign 16
59twop52:
60 .quad 0x4330000000000000
61 .quad 0x0000000000000fff
62
63 .balign 16
64sticky:
65 .quad 0x0000000000000000
66 .long 0x00000012
67
68 .balign 16
69twelve:
70 .long 0x00000000
71
72#define TWOp52 twop52-0b(%ecx)
73#define STICKY sticky-0b(%ecx,%eax,8)
74
75.text
76.balign 4
77DEFINE_COMPILERRT_FUNCTION(__floatundisf)
78 movl 8(%esp), %eax
79 movd 8(%esp), %xmm1
80 movd 4(%esp), %xmm0
81 punpckldq %xmm1, %xmm0
82
83 calll 0f
840: popl %ecx
85 shrl %eax // high 31 bits of input as sint32
86 addl $0x7ff80000, %eax
87 sarl $31, %eax // (big input) ? -1 : 0
88 movsd STICKY, %xmm1 // (big input) ? 0xfff : 0
89 movl $12, %edx
90 andl %eax, %edx // (big input) ? 12 : 0
91 movd %edx, %xmm3
92 andpd %xmm0, %xmm1 // (big input) ? input & 0xfff : 0
93 movsd TWOp52, %xmm2 // 0x1.0p52
94 psrlq %xmm3, %xmm0 // (big input) ? input >> 12 : input
95 orpd %xmm2, %xmm1 // 0x1.0p52 + ((big input) ? input & 0xfff : input)
96 orpd %xmm1, %xmm0 // 0x1.0p52 + ((big input) ? (input >> 12 | input & 0xfff) : input)
97 subsd %xmm2, %xmm0 // (double)((big input) ? (input >> 12 | input & 0xfff) : input)
98 cvtsd2ss %xmm0, %xmm0 // (float)((big input) ? (input >> 12 | input & 0xfff) : input)
99 pslld $23, %xmm3
100 paddd %xmm3, %xmm0 // (float)input
101 movd %xmm0, 4(%esp)
102 flds 4(%esp)
103 ret
104END_COMPILERRT_FUNCTION(__floatundisf)
105
106#endif // __i386__
107
108NO_EXEC_STACK_DIRECTIVE
109
110

source code of compiler-rt/lib/builtins/i386/floatundisf.S