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Use backtick code blocks for syntax highlighting

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James Gregory 2013-12-31 11:38:48 +11:00
commit f658bfbb40
203 changed files with 26546 additions and 25801 deletions
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54
13-02.md
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@ -22,18 +22,22 @@ throughput of two cycles/char."
**LISTING 13.3 L13-3.ASM**
mov bl,[di] ;get the state value for the pair
mov di,[bp+OFFS] ;get the next pair of characters
mov ax,[bx+8000h] ;increment word and line count
add dx,ax ; appropriately for the pair
```nasm
mov bl,[di] ;get the state value for the pair
mov di,[bp+OFFS] ;get the next pair of characters
mov ax,[bx+8000h] ;increment word and line count
add dx,ax ; appropriately for the pair
```
**LISTING 13.4 L13-4.ASM**
mov bl,[di] ;get the state value for the pair
mov di,[bp+OFFS] ;get the next pair of characters
add dx,ax ;increment word and line count
; appropriately for the pair
mov ax,[bx+8000h] ;get increments for next time
```nasm
mov bl,[di] ;get the state value for the pair
mov di,[bp+OFFS] ;get the next pair of characters
add dx,ax ;increment word and line count
; appropriately for the pair
mov ax,[bx+8000h] ;get increments for next time
```
I'd like to point out two fairly remarkable things. First, the single
cycle that Terje saved in Listing 13.4 sped up his entire word-counting
@ -57,9 +61,11 @@ and 16-bit registers are not valid operands.) The obvious use of
first in memory, also called *little endian*) to Motorola format (most
significant byte first in memory, or *big endian*), like so:
lodsd
bswap
stosd
```nasm
lodsd
bswap
stosd
```
**BSWAP** can also be useful for reversing the order of pixel bits from
a bitmap so that they can be rotated 32 bits at a time with an
@ -94,17 +100,19 @@ memory, isn't it?
**LISTING 13.5 L13-5.ASM**
mov cx,[initialskip]
shl ecx,16 ;put skip value in upper half of ECX
mov cx,100 ;put loop count in CX
looptop:
:
ror ecx,16 ;make skip value word accessible in CX
add bx,cx ;skip BX ahead
inc cx ;set next skip value
ror ecx,16 ;put loop count in CX
dec cx ;count down loop
jnz looptop
```nasm
mov cx,[initialskip]
shl ecx,16 ;put skip value in upper half of ECX
mov cx,100 ;put loop count in CX
looptop:
:
ror ecx,16 ;make skip value word accessible in CX
add bx,cx ;skip BX ahead
inc cx ;set next skip value
ror ecx,16 ;put loop count in CX
dec cx ;count down loop
jnz looptop
```
Not necessarily. Shifts and rotates are among the worst performing
instructions of the 486, taking 2 to 3 cycles to execute. Thus, it takes