SHL won't do 32 bits
Red_Dog
Posts: 7
I'm trying to write a shift routine to shift two 32 bit registers to perform a 64 bit shift.
When the shift count is <= 32 I'm doing the following:
Mov temp, #32
Sub temp, count
Mov high_temp, high_long
Shl high_temp, temp
Shr low_long, count
Add low_long, high_temp
Shr high_long, count
The problem I'm having is when temp is 32, shl doesn't shift at all.
If I make temp #31, it works, but not #32. If make
Temp t#33, it shifts it as if temp is #1.
The manual doesn't say anything about limitations for the number of
Bits that can be shifted, although it wouldn't make sense to shift it
More than 32.
What am I missing?
When the shift count is <= 32 I'm doing the following:
Mov temp, #32
Sub temp, count
Mov high_temp, high_long
Shl high_temp, temp
Shr low_long, count
Add low_long, high_temp
Shr high_long, count
The problem I'm having is when temp is 32, shl doesn't shift at all.
If I make temp #31, it works, but not #32. If make
Temp t#33, it shifts it as if temp is #1.
The manual doesn't say anything about limitations for the number of
Bits that can be shifted, although it wouldn't make sense to shift it
More than 32.
What am I missing?
Comments
-Phil
A thought: code the shift using rotates, since a 32 bit and a 0 bit rotate are the same thing anyway.
shifter cmp shiftbits, #64 wc, wz if_ae mov lolong, #0 if_ae mov hilong, #0 if_ae jmp #shifter_ret cmp shiftbits, #32 wc, wz if_e mov hilong, lolong if_e mov lolong, #0 if_e jmp #shifter_ret if_a sub shiftbits, #32 if_a shl hilong, shiftbits if_a mov lolong, #0 if_a jmp #shifter_ret :loop shl lolong, #1 wc rcl hilong, #1 djnz shiftbits, #:loop shifter_ret retshifter cmp shiftbits, #64 wc, wz if_b jmp #:less64 mov lolong, #0 mov hilong, #0 jmp #shifter_ret :less64 rol lolong, shiftbits neg mask, #1 shl mask, shiftbits cmp shiftbits, #32 wc,wz if_b jmp #:less32 mov hilong, lolong and hilong, mask mov lolong, #0 jmp #shifter_ret :less32 shl hilong, shiftbits xor hilong, lolong and lolong, mask xor hilong, lolong shifter_ret retshifter cmpsub shiftbits, #32 wc if_c mov hilong, lolong if_c mov lolong, #0 if_c jmp #shifter rol lolong, shiftbits neg mask, #1 shl mask, shiftbits shl hilong, shiftbits xor hilong, lolong and lolong, mask xor hilong, lolong shifter_ret retshl64 mov hilong,lowlong shl lolong,shftamt cmp shftamt,#32 wc if_nc mov lolong,#0 cmp shftamt,#64 wc neg shftamt,shftamt wz shr hilong,shftamt if_z_or_nc mov hilong,#0 shl64_ret ret-Phil
-Phil