1 //===-- comparesf2.S - Implement single-precision soft-float comparisons --===//
3 // The LLVM Compiler Infrastructure
5 // This file is dual licensed under the MIT and the University of Illinois Open
6 // Source Licenses. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the following soft-fp_t comparison routines:
12 // __eqsf2 __gesf2 __unordsf2
17 // The semantics of the routines grouped in each column are identical, so there
18 // is a single implementation for each, with multiple names.
20 // The routines behave as follows:
22 // __lesf2(a,b) returns -1 if a < b
25 // 1 if either a or b is NaN
27 // __gesf2(a,b) returns -1 if a < b
30 // -1 if either a or b is NaN
32 // __unordsf2(a,b) returns 0 if both a and b are numbers
33 // 1 if either a or b is NaN
35 // Note that __lesf2( ) and __gesf2( ) are identical except in their handling of
38 //===----------------------------------------------------------------------===//
40 #include "../assembly.h"
44 DEFINE_COMPILERRT_FUNCTION(__eqsf2)
45 DEFINE_COMPILERRT_FUNCTION(__lesf2)
46 DEFINE_COMPILERRT_FUNCTION(__ltsf2)
47 DEFINE_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.
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
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.
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.
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
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
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.
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.
94 // Finally, we need to deal with NaNs. If either argument is NaN, replace
95 // the value in r0 with 1.
102 DEFINE_COMPILERRT_FUNCTION(__gesf2)
103 DEFINE_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.
110 orrs r12, r2, r3, lsr #1
113 mvnlo r0, r1, asr #31
114 movhi r0, r1, asr #31
117 cmpls r3, #0xff000000
122 DEFINE_COMPILERRT_FUNCTION(__unordsf2)
123 // Return 1 for NaN values, 0 otherwise.
128 cmpls r3, #0xff000000