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// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
#include "../assembly.h"
// float __floatundisf(du_int a);
// Note that there is a hardware instruction, fildll, that does most of what
// this function needs to do. However, because of our ia32 ABI, it will take
// a write-small read-large stall, so the software implementation here is
// actually several cycles faster.
// This is a branch-free implementation. A branchy implementation might be
// faster for the common case if you know something a priori about the input
// distribution.
/* branch-free x87 implementation - one cycle slower than without x87.
#ifdef __i386__
.const
.align 3
.quad 0x43f0000000000000
twop64: .quad 0x0000000000000000
#define TWOp64 twop64-0b(%ecx,%eax,8)
.text
.align 4
DEFINE_COMPILERRT_FUNCTION(__floatundisf)
movl 8(%esp), %eax
movd 8(%esp), %xmm1
movd 4(%esp), %xmm0
punpckldq %xmm1, %xmm0
calll 0f
0: popl %ecx
sarl $31, %eax
movq %xmm0, 4(%esp)
fildll 4(%esp)
faddl TWOp64
fstps 4(%esp)
flds 4(%esp)
ret
#endif // __i386__
*/
/* branch-free, x87-free implementation - faster at the expense of code size */
#ifdef __i386__
#ifndef __ELF__
.const
.align 3
#else
.align 8
#endif
twop52: .quad 0x4330000000000000
.quad 0x0000000000000fff
sticky: .quad 0x0000000000000000
.long 0x00000012
twelve: .long 0x00000000
#define TWOp52 twop52-0b(%ecx)
#define STICKY sticky-0b(%ecx,%eax,8)
.text
.align 4
DEFINE_COMPILERRT_FUNCTION(__floatundisf)
movl 8(%esp), %eax
movd 8(%esp), %xmm1
movd 4(%esp), %xmm0
punpckldq %xmm1, %xmm0
calll 0f
0: popl %ecx
shrl %eax // high 31 bits of input as sint32
addl $0x7ff80000, %eax
sarl $31, %eax // (big input) ? -1 : 0
movsd STICKY, %xmm1 // (big input) ? 0xfff : 0
movl $12, %edx
andl %eax, %edx // (big input) ? 12 : 0
movd %edx, %xmm3
andpd %xmm0, %xmm1 // (big input) ? input & 0xfff : 0
movsd TWOp52, %xmm2 // 0x1.0p52
psrlq %xmm3, %xmm0 // (big input) ? input >> 12 : input
orpd %xmm2, %xmm1 // 0x1.0p52 + ((big input) ? input & 0xfff : input)
orpd %xmm1, %xmm0 // 0x1.0p52 + ((big input) ? (input >> 12 | input & 0xfff) : input)
subsd %xmm2, %xmm0 // (double)((big input) ? (input >> 12 | input & 0xfff) : input)
cvtsd2ss %xmm0, %xmm0 // (float)((big input) ? (input >> 12 | input & 0xfff) : input)
pslld $23, %xmm3
paddd %xmm3, %xmm0 // (float)input
movd %xmm0, 4(%esp)
flds 4(%esp)
ret
#endif // __i386__
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