57 lines
1.3 KiB
ArmAsm
57 lines
1.3 KiB
ArmAsm
#
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.sect .text; .sect .rom; .sect .data; .sect .bss
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/* Split a double-precision float into fraction and exponent, like
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* frexp(3) in C, http://en.cppreference.com/w/c/numeric/math/frexp
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*
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* Stack: ( double -- fraction exponent )
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*/
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#define DBL_EXPBITS 11
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#define DBL_FRACHBITS 20
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#define DBL_FRACLBITS 32
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#define DBL_FRACBITS 52
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#define DBL_EXP_INFNAN 2047
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#define DBL_EXP_BIAS 1023
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.sect .text
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.define .fef8
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.fef8:
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lw r4, 0(sp) ! r4 = low word (bits 0..31)
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lw r5, 4(sp) ! r5 = high word (bits 32..63)
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! IEEE double = sign * 1.fraction * 2**(exponent - 1023)
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! sign exponent fraction
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! 31 30..19 18..0, 31..0
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!
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! IEEE exponent = 1022 in [0.5, 1) or (-1, -0.5].
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ext r7, r5, DBL_FRACHBITS, DBL_EXPBITS ! r7 = IEEE exponent
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beq r7, zero, zeroexp ! this number is zero or denormalised, treat specially
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nop
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li at, DBL_EXP_INFNAN
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beq r7, at, return ! just return if infinity or NaN
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nop
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addiu r7, r7, -[DBL_EXP_BIAS-1] ! undo exponent bias
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li at, DBL_EXP_BIAS-1
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ins r5, at, DBL_FRACHBITS, DBL_EXPBITS ! replace exponent
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return:
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addiu sp, sp, -4 ! returning one more quad than we got
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sw r5, 8(sp)
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sw r6, 4(sp)
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sw r7, 0(sp)
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jr ra
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nop
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/* We received a denormalised number or zero. */
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zeroexp:
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/* TODO: we just assume that the number is zero here. */
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mov r5, zero
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mov r6, zero
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mov r7, zero
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b return
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nop
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