1//===-- comparesf2.S - Implement single-precision soft-float comparisons --===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is dual licensed under the MIT and the University of Illinois Open
6// Source Licenses. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the following soft-fp_t comparison routines:
11//
12//   __eqsf2   __gesf2   __unordsf2
13//   __lesf2   __gtsf2
14//   __ltsf2
15//   __nesf2
16//
17// The semantics of the routines grouped in each column are identical, so there
18// is a single implementation for each, with multiple names.
19//
20// The routines behave as follows:
21//
22//   __lesf2(a,b) returns -1 if a < b
23//                         0 if a == b
24//                         1 if a > b
25//                         1 if either a or b is NaN
26//
27//   __gesf2(a,b) returns -1 if a < b
28//                         0 if a == b
29//                         1 if a > b
30//                        -1 if either a or b is NaN
31//
32//   __unordsf2(a,b) returns 0 if both a and b are numbers
33//                           1 if either a or b is NaN
34//
35// Note that __lesf2( ) and __gesf2( ) are identical except in their handling of
36// NaN values.
37//
38//===----------------------------------------------------------------------===//
39
40#include "../assembly.h"
41.syntax unified
42
43.align 2
44DEFINE_COMPILERRT_FUNCTION(__eqsf2)
45DEFINE_COMPILERRT_FUNCTION(__lesf2)
46DEFINE_COMPILERRT_FUNCTION(__ltsf2)
47DEFINE_COMPILERRT_FUNCTION(__nesf2)
48    // Make copies of a and b with the sign bit shifted off the top.  These will
49    // be used to detect zeros and NaNs.
50    mov     r2,         r0, lsl #1
51    mov     r3,         r1, lsl #1
52
53    // We do the comparison in three stages (ignoring NaN values for the time
54    // being).  First, we orr the absolute values of a and b; this sets the Z
55    // flag if both a and b are zero (of either sign).  The shift of r3 doesn't
56    // effect this at all, but it *does* make sure that the C flag is clear for
57    // the subsequent operations.
58    orrs    r12,    r2, r3, lsr #1
59
60    // Next, we check if a and b have the same or different signs.  If they have
61    // opposite signs, this eor will set the N flag.
62    eorsne  r12,    r0, r1
63
64    // If a and b are equal (either both zeros or bit identical; again, we're
65    // ignoring NaNs for now), this subtract will zero out r0.  If they have the
66    // same sign, the flags are updated as they would be for a comparison of the
67    // absolute values of a and b.
68    subspl  r0,     r2, r3
69
70    // If a is smaller in magnitude than b and both have the same sign, place
71    // the negation of the sign of b in r0.  Thus, if both are negative and
72    // a > b, this sets r0 to 0; if both are positive and a < b, this sets
73    // r0 to -1.
74    //
75    // This is also done if a and b have opposite signs and are not both zero,
76    // because in that case the subtract was not performed and the C flag is
77    // still clear from the shift argument in orrs; if a is positive and b
78    // negative, this places 0 in r0; if a is negative and b positive, -1 is
79    // placed in r0.
80    mvnlo   r0,         r1, asr #31
81
82    // If a is greater in magnitude than b and both have the same sign, place
83    // the sign of b in r0.  Thus, if both are negative and a < b, -1 is placed
84    // in r0, which is the desired result.  Conversely, if both are positive
85    // and a > b, zero is placed in r0.
86    movhi   r0,         r1, asr #31
87
88    // If you've been keeping track, at this point r0 contains -1 if a < b and
89    // 0 if a >= b.  All that remains to be done is to set it to 1 if a > b.
90    // If a == b, then the Z flag is set, so we can get the correct final value
91    // into r0 by simply or'ing with 1 if Z is clear.
92	orrne	r0,     r0, #1
93
94    // Finally, we need to deal with NaNs.  If either argument is NaN, replace
95    // the value in r0 with 1.
96    cmp     r2,         #0xff000000
97    cmpls   r3,         #0xff000000
98    movhi   r0,         #1
99    bx      lr
100
101.align 2
102DEFINE_COMPILERRT_FUNCTION(__gesf2)
103DEFINE_COMPILERRT_FUNCTION(__gtsf2)
104    // Identical to the preceeding except in that we return -1 for NaN values.
105    // Given that the two paths share so much code, one might be tempted to
106    // unify them; however, the extra code needed to do so makes the code size
107    // to performance tradeoff very hard to justify for such small functions.
108    mov     r2,         r0, lsl #1
109    mov     r3,         r1, lsl #1
110    orrs    r12,    r2, r3, lsr #1
111    eorsne  r12,    r0, r1
112    subspl  r0,     r2, r3
113    mvnlo   r0,         r1, asr #31
114    movhi   r0,         r1, asr #31
115	orrne	r0,     r0, #1
116    cmp     r2,         #0xff000000
117    cmpls   r3,         #0xff000000
118    movhi   r0,         #-1
119    bx      lr
120
121.align 2
122DEFINE_COMPILERRT_FUNCTION(__unordsf2)
123    // Return 1 for NaN values, 0 otherwise.
124    mov     r2,         r0, lsl #1
125    mov     r3,         r1, lsl #1
126    mov     r0,         #0
127    cmp     r2,         #0xff000000
128    cmpls   r3,         #0xff000000
129    movhi   r0,         #1
130    bx      lr
131