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Diffstat (limited to 'lib/arm/comparesf2.S')
| -rw-r--r-- | lib/arm/comparesf2.S | 130 |
1 files changed, 130 insertions, 0 deletions
diff --git a/lib/arm/comparesf2.S b/lib/arm/comparesf2.S new file mode 100644 index 000000000000..f21e0bcd13f6 --- /dev/null +++ b/lib/arm/comparesf2.S @@ -0,0 +1,130 @@ +//===-- comparesf2.S - Implement single-precision soft-float comparisons --===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file implements the following soft-fp_t comparison routines: +// +// __eqsf2 __gesf2 __unordsf2 +// __lesf2 __gtsf2 +// __ltsf2 +// __nesf2 +// +// The semantics of the routines grouped in each column are identical, so there +// is a single implementation for each, with multiple names. +// +// The routines behave as follows: +// +// __lesf2(a,b) returns -1 if a < b +// 0 if a == b +// 1 if a > b +// 1 if either a or b is NaN +// +// __gesf2(a,b) returns -1 if a < b +// 0 if a == b +// 1 if a > b +// -1 if either a or b is NaN +// +// __unordsf2(a,b) returns 0 if both a and b are numbers +// 1 if either a or b is NaN +// +// Note that __lesf2( ) and __gesf2( ) are identical except in their handling of +// NaN values. +// +//===----------------------------------------------------------------------===// + +#include "../assembly.h" +.syntax unified + +.align 2 +DEFINE_COMPILERRT_FUNCTION(__eqsf2) +DEFINE_COMPILERRT_FUNCTION(__lesf2) +DEFINE_COMPILERRT_FUNCTION(__ltsf2) +DEFINE_COMPILERRT_FUNCTION(__nesf2) + // Make copies of a and b with the sign bit shifted off the top. These will + // be used to detect zeros and NaNs. + mov r2, r0, lsl #1 + mov r3, r1, lsl #1 + + // We do the comparison in three stages (ignoring NaN values for the time + // being). First, we orr the absolute values of a and b; this sets the Z + // flag if both a and b are zero (of either sign). The shift of r3 doesn't + // effect this at all, but it *does* make sure that the C flag is clear for + // the subsequent operations. + orrs r12, r2, r3, lsr #1 + + // Next, we check if a and b have the same or different signs. If they have + // opposite signs, this eor will set the N flag. + eorsne r12, r0, r1 + + // If a and b are equal (either both zeros or bit identical; again, we're + // ignoring NaNs for now), this subtract will zero out r0. If they have the + // same sign, the flags are updated as they would be for a comparison of the + // absolute values of a and b. + subspl r0, r2, r3 + + // If a is smaller in magnitude than b and both have the same sign, place + // the negation of the sign of b in r0. Thus, if both are negative and + // a > b, this sets r0 to 0; if both are positive and a < b, this sets + // r0 to -1. + // + // This is also done if a and b have opposite signs and are not both zero, + // because in that case the subtract was not performed and the C flag is + // still clear from the shift argument in orrs; if a is positive and b + // negative, this places 0 in r0; if a is negative and b positive, -1 is + // placed in r0. + mvnlo r0, r1, asr #31 + + // If a is greater in magnitude than b and both have the same sign, place + // the sign of b in r0. Thus, if both are negative and a < b, -1 is placed + // in r0, which is the desired result. Conversely, if both are positive + // and a > b, zero is placed in r0. + movhi r0, r1, asr #31 + + // If you've been keeping track, at this point r0 contains -1 if a < b and + // 0 if a >= b. All that remains to be done is to set it to 1 if a > b. + // If a == b, then the Z flag is set, so we can get the correct final value + // into r0 by simply or'ing with 1 if Z is clear. + orrne r0, r0, #1 + + // Finally, we need to deal with NaNs. If either argument is NaN, replace + // the value in r0 with 1. + cmp r2, #0xff000000 + cmpls r3, #0xff000000 + movhi r0, #1 + bx lr + +.align 2 +DEFINE_COMPILERRT_FUNCTION(__gesf2) +DEFINE_COMPILERRT_FUNCTION(__gtsf2) + // Identical to the preceeding except in that we return -1 for NaN values. + // Given that the two paths share so much code, one might be tempted to + // unify them; however, the extra code needed to do so makes the code size + // to performance tradeoff very hard to justify for such small functions. + mov r2, r0, lsl #1 + mov r3, r1, lsl #1 + orrs r12, r2, r3, lsr #1 + eorsne r12, r0, r1 + subspl r0, r2, r3 + mvnlo r0, r1, asr #31 + movhi r0, r1, asr #31 + orrne r0, r0, #1 + cmp r2, #0xff000000 + cmpls r3, #0xff000000 + movhi r0, #-1 + bx lr + +.align 2 +DEFINE_COMPILERRT_FUNCTION(__unordsf2) + // Return 1 for NaN values, 0 otherwise. + mov r2, r0, lsl #1 + mov r3, r1, lsl #1 + mov r0, #0 + cmp r2, #0xff000000 + cmpls r3, #0xff000000 + movhi r0, #1 + bx lr |